HAST and ZFS with CARP failover

gkontos

gkontos

HAST (Highly Available Storage) is a new concept for FreeBSD and it is under constant development. HAST allows to transparently store data on two physically separated machines connected over the TCP/IP network. HAST operates on block level making it transparent for file systems, providing disk-like devices in /dev/hast directory.

In this article we will create two identical HAST nodes, hast1 and hast2. Both devices will use one NIC connected to a vlan for data synchronization and another NIC will be configured via CARP in order to share the same IP address across the network. The first node will be called storage1.hast.test, the second storage2.hast.test and they will both listen to a common IP address which we will bind to storage.hast.test

HAST binds its resource names according to the machine's hostname. Therefore, we will use hast1.freebsd.loc and hast2.freebsd.loc as the machines hostnames so that HAST can operate without complaining.

For starters, lets set up two identical nodes. For this example I have installed FreeBSD 9.0-RELEASE on two deferent instances using a Linux KVM. Both nodes have 512MB of RAM, one SATA drive containing the OS and three SATA drives which will be used to create our shared Raidz1 pool.

In order for carp to work we don't have to compile a new kernel. We can just load it as a module by adding to /boot/loader.conf

Code: 
 if_carp_load="YES"

Our both nodes are set up, it is time to make some adjustments. First a descent /etc/rc.conf for the first node:

Code: 
zfs_enable="YES"

###Primary Interface##
ifconfig_re0="inet 10.10.10.181  netmask 255.255.255.0"

###Secondary Interface for HAST###
ifconfig_re1="inet 192.168.100.100  netmask 255.255.255.0"

defaultrouter="10.10.10.1"
sshd_enable="YES"
hostname="hast1.freebsd.loc"

##CARP INTERFACE SETUP##
cloned_interfaces="carp0"
ifconfig_carp0="inet 10.10.10.180 netmask 255.255.255.0 vhid 1 pass mypassword advskew 0"

hastd_enable=YES

The second node we will also much the first except for the IP addressing:

Code: 
zfs_enable="YES"

###Primary Interface##
ifconfig_re0="inet 10.10.10.182  netmask 255.255.255.0"

###Secondary Interface for HAST###
ifconfig_re1="inet 192.168.100.101  netmask 255.255.255.0"

defaultrouter="10.10.10.1"
sshd_enable="YES"
hostname="hast2.freebsd.loc"

##CARP INTERFACE SETUP##
cloned_interfaces="carp0"
ifconfig_carp0="inet 10.10.10.180 netmask 255.255.255.0 vhid 1 pass mypassword advskew 0"

hastd_enable=YES

At this point we have assigned re1 with two IPs for HAST synchronization. We have also assigned two IPs to re0 which in turn we share with a third common IP assigned to carp0.
As a result, re1 is being used for HAST synchronization in a vlan while carp0 which is cloned by re0 used under the same vlan with the rest of our clients.

In order for HAST to function correctly we have to resolve the correct IPs on every node. We don't want to rely on DNS for this because DNS can fail. Instead we will use /etc/hosts same on every node.

Code: 
::1			localhost localhost.freebsd.loc
127.0.0.1		localhost localhost.freebsd.loc
192.168.100.100		hast1.freebsd.loc hast1
192.168.100.101		hast2.freebsd.loc hast2

10.10.10.181          	storage1.hast.test storage1
10.10.10.182          	storage2.hast.test storage2
10.10.10.180	      	storage.hast.test  storage

Next, we have to create the /etc/hast.conf file. Here we will declare the resources that we want to create. All resources will eventually create devices located under /dev/hast on the primary node. Every resource indicates a physical device specifying a local and remote IP device. The /etc/hast.conf must be exactly the same on every node.

Code: 
resource disk1 {
        on hast1 {
                local /dev/ad1
                remote hast2
        }
        on  hast2 {
                local /dev/ad1
                remote hast1
        }
}

resource disk2 {
        on  hast1 {
                local /dev/ad2
                remote hast2
        }
        on  hast2 {
                local /dev/ad2
                remote hast1
        }
}

resource disk3 {
        on  hast1 {
                local /dev/ad3
                remote hast2
        }
        on  hast2 {
                local /dev/ad3
                remote hast1
        }
}

In this example we are sharing three resources, disk1, disk2 and disk3. Each resource indicates a device the local and the remote IP address. With this configuration in place, we are ready to begin setting up out HAST devices.

Lets start hastd on both nodes first:

Code: 
hast1#/etc/rc.d/hastd start
Code: 
hast2#/etc/rc.d/hastd start

Now on the primary node we will initialize our resources, create them and finally assign a primary role:

Code: 
hast1#hastctl role init disk1
hast1#hastctl role init disk2
hast1#hastctl role init disk3
hast1#hastctl create disk1
hast1#hastctl create disk2
hast1#hastctl create disk3
hast1#hastctl role primary disk1
hast1#hastctl role primary disk2
hast1#hastctl role primary disk3

Next, on the secondary node we will initialize our resources, create them and finally assign a secondary role:

Code: 
hast2#hastctl role init disk1
hast2#hastctl role init disk2
hast2#hastctl role init disk3
hast2#hastctl create disk1
hast2#hastctl create disk2
hast2#hastctl create disk3
hast2#hastctl role secondary disk1
hast2#hastctl role secondary disk2
hast2#hastctl role secondary disk3

There are other ways for creating and assigning roles to each resource. Having repeat this procedure a few times, I saw that this usually always works.

Now check the status on both nodes:

Code: 
hast1# hastctl status
disk1:
  role: primary
  provname: disk1
  localpath: /dev/ada1
  ...
  remoteaddr: hast2
  replication: fullsync
  status: complete
  dirty: 0 (0B)
  ...
disk2:
  role: primary
  provname: disk2
  localpath: /dev/ada2
  ...
  remoteaddr: hast2
  replication: fullsync
  status: complete
  dirty: 0 (0B)
  ...
disk3:
  role: primary
  provname: disk3
  localpath: /dev/ada3
  ...
  remoteaddr: hast2
  replication: fullsync
  status: complete
  dirty: 0 (0B)
  ...

The first node looks good. Status is complete.

Code: 
hast2# hastctl status
disk1:
  role: secondary
  provname: disk1
  localpath: /dev/ada1
  ...
  remoteaddr: hast1
  replication: fullsync
  status: complete
  dirty: 0 (0B)
  ...
disk2:
  role: secondary
  provname: disk2
  localpath: /dev/ada2
  ...
  remoteaddr: hast1
  replication: fullsync
  status: complete
  dirty: 0 (0B)
  ...
disk3:
  role: secondary
  provname: disk3
  localpath: /dev/ada3
  ...
  remoteaddr: hast1
  replication: fullsync
  status: complete
  dirty: 0 (0B)
  ...

So does the second. Like I mentioned earlier there are different ways for doing this the first time. You have to look for the word
status: complete. If you get a degraded status you can always repeat the procedure.

Now it is time to create our ZFS pool. The primary node should have a /dev/hast directory containing our resources. This directory appears only at the active node.

Code: 
hast1# zpool create zhast raidz1 /dev/hast/disk1 /dev/hast/disk2 /dev/hast/disk3
hast1# zpool status zhast
 pool: zhast
 state: ONLINE
 scan: none requested
 config:

	NAME            STATE     READ WRITE CKSUM
	zhast           ONLINE       0     0     0
	  raidz1-0      ONLINE       0     0     0
	    hast/disk1  ONLINE       0     0     0
	    hast/disk2  ONLINE       0     0     0
	    hast/disk3  ONLINE       0     0     0

We can now use hastctl status on each node to see if everything looks ok. The magic word we are looking for here is:
replication: fullsync

At this point both of our nodes should be available for failover. We have storage1 running as primary and sharing a pool called zhast. Our storage2 is currently in a standby mode. If we have set DNS properly we can ssh to storage.hast.test or by using its carp IP to 10.10.10.180.
 
HAST and ZFS with CARP failover (Part2)

In order to perform a failover we have to first export our pool from the first node, change the role of each resource to secondary. Then change the role of each resource to primary on the standby node and import the pool. This procedure will be done manually to test if failover really works. But for a real HA solution we will eventually create a script that will take care of this.

First lets export our pool and change our resources role:

Code: 
hast1# zpool export zhast
hast1# hastctl role secondary disk1
hast1# hastctl role secondary disk2
hast1# hastctl role secondary disk3

Now, lets reverse the procedure on the standby node:

Code: 
hast2# hastctl role primary disk1
hast2# hastctl role primary disk2
hast2# hastctl role primary disk3
hast2# zpool import zhast

The roles have successfully changed, lets see our pool status:

Code: 
hast2# zpool status zhast
 pool: zhast
 state: ONLINE
 scan: none requested
 config:

	NAME            STATE     READ WRITE CKSUM
	zhast           ONLINE       0     0     0
	  raidz1-0      ONLINE       0     0     0
	    hast/disk1  ONLINE       0     0     0
	    hast/disk2  ONLINE       0     0     0
	    hast/disk3  ONLINE       0     0     0

errors: No known data errors

Again, by using hastctl status on each node we can verify that the roles have indeed changed and that the status is complete. This is a sample output from the second node now in charge:

Code: 
hast2# hastctl status
disk1:
  role: primary
  provname: disk1
  localpath: /dev/ad1
  ...
  remoteaddr: hast1
  replication: fullsync
  status: complete
  ...
disk2:
  role: primary
  provname: disk2
  localpath: /dev/ad2
  ...
  remoteaddr: hast1
  replication: fullsync
  status: complete
  ...
disk3:
  role: primary
  provname: disk3
  localpath: /dev/ad3
  ...
  remoteaddr: hast1
  replication: fullsync
  status: complete
  ...

It is now time to automate this procedure. When do we want our servers to automatically failover?
One reason would be if the primary node is not responding to the external network thus not being able to serve its clients. Using a devd event we can catch a carp interface going up or down and a state change.

Add the following lines to /etc/devd.conf on both nodes:

Code: 
notify 30 {
	match "system" "IFNET";
	match "subsystem" "carp0";
	match "type" "LINK_UP";
	action "/usr/local/bin/failover master";
};

notify 30 {
	match "system" "IFNET";
	match "subsystem" "carp0";
	match "type" "LINK_DOWN";
	action "/usr/local/bin/failover slave";
};

And now lets create the failover script which will be responsible for doing automatically what we did before manually:

Code: 
#!/bin/sh

# Original script by Freddie Cash <fjwcash@gmail.com>
# Modified by Michael W. Lucas <mwlucas@BlackHelicopters.org>
# and Viktor Petersson <vpetersson@wireload.net>
# Modified by George Kontostanos <gkontos.mail@gmail.com>

# The names of the HAST resources, as listed in /etc/hast.conf
resources="disk1 disk2 disk3"

# delay in mounting HAST resource after becoming master
# make your best guess
delay=3

# logging
log="local0.debug"
name="failover"
pool="zhast"

# end of user configurable stuff

case "$1" in
	master)
		logger -p $log -t $name "Switching to primary provider for ${resources}."
		sleep ${delay}

		# Wait for any "hastd secondary" processes to stop
		for disk in ${resources}; do
			while $( pgrep -lf "hastd: ${disk} \(secondary\)" > /dev/null 2>&1 ); do
				sleep 1
			done

			# Switch role for each disk
			hastctl role primary ${disk}
			if [ $? -ne 0 ]; then
				logger -p $log -t $name "Unable to change role to primary for resource ${disk}."
				exit 1
			fi
		done

		# Wait for the /dev/hast/* devices to appear
		for disk in ${resources}; do
			for I in $( jot 60 ); do
				[ -c "/dev/hast/${disk}" ] && break
				sleep 0.5
			done

			if [ ! -c "/dev/hast/${disk}" ]; then
				logger -p $log -t $name "GEOM provider /dev/hast/${disk} did not appear."
				exit 1
			fi
		done

		logger -p $log -t $name "Role for HAST resources ${resources} switched to primary."


		logger -p $log -t $name "Importing Pool"
		# Import ZFS pool. Do it forcibly as it remembers hostid of
                # the other cluster node.
                out=`zpool import -f "${pool}" 2>&1`
                if [ $? -ne 0 ]; then
                    logger -p local0.error -t hast "ZFS pool import for resource ${resource} failed: ${out}."
                    exit 1
                fi
                logger -p local0.debug -t hast "ZFS pool for resource ${resource} imported."

	;;

	slave)
		logger -p $log -t $name "Switching to secondary provider for ${resources}."

		# Switch roles for the HAST resources
		zpool list | egrep -q "^${pool} "
        	if [ $? -eq 0 ]; then
                	# Forcibly export file pool.
                	out=`zpool export -f "${pool}" 2>&1`
               		 if [ $? -ne 0 ]; then
                        	logger -p local0.error -t hast "Unable to export pool for resource ${resource}: ${out}."
                        	exit 1
                	 fi
                	logger -p local0.debug -t hast "ZFS pool for resource ${resource} exported."
        	fi
		for disk in ${resources}; do
			sleep $delay
			hastctl role secondary ${disk} 2>&1
			if [ $? -ne 0 ]; then
				logger -p $log -t $name "Unable to switch role to secondary for resource ${disk}."
				exit 1
			fi
			logger -p $log -t $name "Role switched to secondary for resource ${disk}."
		done
	;;
esac

Let's try it and see if it works. Log into both the currently active and standby node. Make sure that you are on the active by issuing a hastctl status command. Then force a failover by bringing the interface which is associated with carp0 down.

Code: 
hast1# ifconfig er0 down

Watch at the generated messages:

Code: 
hast1# tail -f /var/log/debug.log

Feb  6 15:01:41 hast1 failover: Switching to secondary provider for disk1 disk2 disk3.
Feb  6 15:01:49 hast1 hast: ZFS pool for resource  exported.
Feb  6 15:01:52 hast1 failover: Role switched to secondary for resource disk1.
Feb  6 15:01:55 hast1 failover: Role switched to secondary for resource disk2.
Feb  6 15:01:58 hast1 failover: Role switched to secondary for resource disk3.

Code: 
hast2# tail -f /var/log/debug.log

Feb  6 15:02:15 hast2 failover: Switching to primary provider for disk1 disk2 disk3.
Feb  6 15:02:19 hast2 failover: Role for HAST resources disk1 disk2 disk3 switched to primary.
Feb  6 15:02:19 hast2 failover: Importing Pool
Feb  6 15:02:52 hast2 hast: ZFS pool for resource  imported.

Voila! The failover worked like a charm and now hast2 has assumed the primary role.


Further considerations:​

What we did today is a basic setup of two nodes sharing a raidz1 pool with automatic role failover in case of a failure that would result in a loss of a carp interface.

Obviously, a similar devd event would be generated in case we loose a HAST replication interface. This is something that needs to be addressed similarly since losing that interface will leave us with no synchronization at all.

Going further, we would have to add scripts that will bring up and down services during a failover.

Original article: http://www.aisecure.net/2012/02/07/hast-freebsd-zfs-with-carp-failover/
Resources: MICHAEL W LUCAS, The Freebsd Handbook
 
Did you also test a sudden reboot of the master? If I do this, then I get in all kinds of trouble.

Mainly because the CARP interface starts in master mode after a reboot and hence will execute the master script, even if it is not master. Then the trouble starts and you get a split brain scenario.

Regards,
Johan
 
Sylhouette said:
Did you also test a sudden reboot of the master.
If i do this, then i get in all kind of troubles.

Mainly because the carp interface starts in master mode after a reboot and hence will execute the master script, even if it is not master.
Then the trouble starts and you get a split brain scenario.

regards
Johan
Click to expand...

I did some tests running net/samba36 with both machines sharing /zhast. File sharing service was enabled in both machines.

The connection was established via the CARP IP. During the reboot of the master there was an obvious delay until the pool becomes available to the secondary machine but that was solved by a client reset.

After the node came up, CARP did not assign the master role therefore I always had to perform a manual fail back.

Which FreeBSD version are you using?
Do you by any chance have net.inet.carp.preempt=1 in your /etc/sysctl.conf?
 
Sylhouette said:
Did you also test a sudden reboot of the master? If I do this, then I get in all kinds of trouble.

Mainly because the CARP interface starts in master mode after a reboot and hence will execute the master script, even if it is not master. Then the trouble starts and you get a split brain scenario.
Click to expand...

This is a known bug with CARP and is being worked on. The interim fix is to not enable the preempt sysctl for CARP.
 
Great work!
There is a little typo, but it doesn´t affect the script. Look for ${resource} which should be ${resources}.
 
hast or not hast

I've been using a version of this guide to set up my own replication testing in two Xen guests. Having disk1 and disk2 set up in HAST I've created a pool with mirror devices. This works most of the time, and all of the time if everything is shut down cleanly.

But for testing I've also tried resetting the HAST master in the middle of writing to a new file, which can get me into troubles. Once the ZFS metadata got corrupted which meant it rolled back a couple of minutes after forcing import with zfs import -F.

Another time it completely locks up on zfs import with state tx->tx. Rendering all zfs tools unusable since they all lock up and wait for this import. The same thing happens on both machines even after reboots etc.

So I'm currently wondering if this method really is reliable enough or if I should go the snapshot sync route without HAST.
 
If you forcibly export a pool during heavy I/O operations then you will eventually end up with corrupted metadata.

This means that you should never initiate a manual failover during I/O operations.

What happens though if the primary node crashes?

The secondary node will try to import the pool and most probably it will unless a heave corruption has occurred. In that case you can use different import techniques and heal the pool.
 
In my recent tests I've simply done ifconfig down or hard reset while a client is copying files to it via NFS.

More than once I've gotten metadata corruption and errors which when trying zfs import -F tells me to restore the pool from a backup and refuses to import it.

Seems a bit sketchy to me as the whole point of doing this in my case is to have a reliable backup machine in case the primary burns up. Also to stall NFS clients until the secondary comes up, which works as long as ZFS doesn't get corrupted.

But I have only tried this in a virtual environment using this setup:
  • two virtual machines running with 1G of ram as Xen guests.
  • two ZFS mirrored virtual drives via hast devices.
  • CARP setup which is monitored by devd and that executes my script similar to the one in the article, with additions to start/stop nfsd.
Also I'm having these errors which might break things:
Code: 
Mar 29 10:01:01 storage1 hastd[6690]: [disk2] (primary) Remote request failed (Operation not supported by device): FLUSH.
Mar 29 10:01:02 storage1 hastd[6690]: [disk2] (primary) Unable to flush disk cache on activemap update: Operation not supported by device.

My idea was to apply this on real machines with raidz of 3 drives, which later would be expanded by an additional three drives. I'm wondering if anyone has used this setup on real machines and in production?
 
Hello,
I am interested too in this setup. I have tried it before with linux/pacemaker and I ask these questions:

1) When I import/export a zfs from master to slave also nfs/cifs setup is imported/exported?

2) Latency of slave server kills write performance (at least with linux/drbd). I plan to put on slave server a battery backupped ram hard disk. Can I tell zfs to use it as zil/log and always write on it, then later copy to zfs volume (slave hdds may for example on standby)

3) Is hast stable?

Thanks,
Mario
 
mgiammarco said:
2) Latency of slave server kills write performance (at least with linux/drbd). I plan to put on slave server a battery backupped ram hard disk. Can I tell zfs to use it as zil/log and always write on it, then later copy to zfs volume (slave hdds may for example on standby)
Click to expand...
Sorry I made a mistake. ZFS does not replicate data to slave. I need that HAST can quickly copy data to a log and then to HDDs.
 
@mgiammarco,

1) During a failover the resources change roles. This means that your storage becomes unavailable in machine#1 and available in machine#2. Please note that the resources can only be available to one machine only, the primary. This means that some services that depend on that data might complain. So, you might need to start /stop those servers as well.

2) I don't understand.

3) This is very difficult to answer. Why? Because until a technology is used enough, then there is not much of user feedback and error reporting.
 
balboah said:
In my recent tests I've simply done ifconfig down or hard reset while a client is copying files to it via NFS.

More than once I've gotten metadata corruption and errors which when trying zfs import -F tells me to restore the pool from a backup and refuses to import it.

Seems a bit sketchy to me as the whole point of doing this in my case is to have a reliable backup machine in case the primary burns up. Also to stall NFS clients until the secondary comes up, which works as long as ZFS doesn't get corrupted.

But I have only tried this in a virtual environment using this setup:
  • two virtual machines running with 1G of ram as Xen guests.
  • two ZFS mirrored virtual drives via hast devices.
  • CARP setup which is monitored by devd and that executes my script similar to the one in the article, with additions to start/stop nfsd.
Also I'm having these errors which might break things:
Code: 
Mar 29 10:01:01 storage1 hastd[6690]: [disk2] (primary) Remote request failed (Operation not supported by device): FLUSH.
Mar 29 10:01:02 storage1 hastd[6690]: [disk2] (primary) Unable to flush disk cache on activemap update: Operation not supported by device.

My idea was to apply this on real machines with raidz of 3 drives, which later would be expanded by an additional three drives. I'm wondering if anyone has used this setup on real machines and in production?
Click to expand...


Narrowing down my issue:

In my virtual Xen environment I get some kind of deadlock with state "tx->tx" and 99.8% idle if I do these steps, also all zfs commands stop working and I'm unable to import the pool again even after a reset of the guest machine:

dd if=/dev/urandom of=./foo bs=100M count=10 &
zpool export -f storage

This only occurs when using HAST in between, not if I create the pool directly on the virtual drives. However it doesn't seem to occur on my real machine that I'm testing with now. Perhaps it's just a bug from using the virtual environment
 
balboah said:
Narrowing down my issue:

In my virtual Xen environment I get some kind of deadlock with state "tx->tx" and 99.8% idle if I do these steps, also all zfs commands stop working and I'm unable to import the pool again even after a reset of the guest machine:

dd if=/dev/urandom of=./foo bs=100M count=10 &
zpool export -f storage

This only occurs when using HAST in between, not if I create the pool directly on the virtual drives. However it doesn't seem to occur on my real machine that I'm testing with now. Perhaps it's just a bug from using the virtual environment
Click to expand...

This could be an expected behavior for ZFS running on top of a virtual machine given the COW nature. Did you allocate full space to the VMs before conducting the tests?
 
gkontos said:
This could be an expected behavior for ZFS running on top of a virtual machine given the COW nature. Did you allocate full space to the VMs before conducting the tests?
Click to expand...

Actually I get the same behaviour with "tx->tx" lockup for a long while on the real servers as well but that at least recovers from it. I haven't gotten the same issue yet of where it's impossible to import the pool again.

However when split-brain occurs, hastctl says 1.8TB of "dirty" instead of 1-2G that is actually written in total. Is there a way around this?

systat -io says tps: 500+ and about 60MB/s on all three drives. While network activity is going at 500KB/s and the dirty counter in hastctl isn't shrinking that fast either. What's causing all the disk activity?
 
@gkontos: Great stuff you shared. :-)

In Linux, DRBD failover is possible with a single NIC, but

  1. How does it look with HAST with a single NIC with your configurations? What configuration changes are needed if it is possible in your configuration samples above?
  2. Could the two HAST nodes be in two different remote locations, I meant not in the same localnet?

I know that a single NIC is not a failover option, but for the system which lacks expansion slots for NICs, one has to opt for a single NIC.
 
zennybsd said:
1) how does it look with HAST with a single NIC with your configurations? What configuration changes are needed if it is possible in your configuration samples above?
Click to expand...

CARP uses only one NIC in this example. The second NIC is used for data replication. You could use only one NIC and just change the resource names.

zennybsd said:
2) could the two HAST nodes be in two different remote locations, I meant not in the same localnet?
Click to expand...

Don't forget that both servers should bind to the same IP address in CARP. This means that you would have to perform some sort of complex ROUTING.
 
@gkontos: Thanks!

From what you said about CARP, it seems that HAST+CARP is good for storage scalability rather than redundancy, right?

Generally, for enterprise grade operations are done in at least two datacenters keeping in mind if something happens (like fire, earthquake or flood etc.) to one datacenter, the IT operations will switchover to the other one in a different geographical location.

Is there any solution of the kind with HAST+CARP or is it only local solution? In GNU/Linux, DRBD with Heartbeat/Corosync is able to do what I stated.

Is that a possibility with HAST? Just curious!
 
zennybsd said:
@gkontos: Thanks!

From what you said about CARP, it seems that HAST+CARP is good for storage scalability rather than redundancy, right?
Click to expand...

Well, it is more for High Available Storage solutions. Meaning that I need my storage space always online.

zennybsd said:
Generally, for enterprise grade operations are done in at least two datacenters keeping in mind if something happens (like fire, earthquake or flood etc.) to one datacenter, the IT operations will switchover to the other one in a different geographical location.
Click to expand...

I don't think HAST would fit into a DR category solution yet. In that case, incremental snapshots would work better.

zennybsd said:
Is there any solution of the kind with HAST+CARP or is it only local solution? In GNU/Linux, DRBD with Heartbeat/Corosync is able to do what I stated.

Is that a possibility with HAST? Just curious!
Click to expand...

It would if HAST were to support asynchronous replication. For the time being only fullsync is supported. I believe that DRDB uses asynchronous replication for long distance clusters.

Also, CARP is not mandatory for HAST. If HAST could support async replication then that would work as a solution for DR replication.
 
DRBD + Heartbeat/Pacemaker or Corosync in GNU/Linux supports synchronous replication too. Maybe such a setup requires a fencing device for more effective implementation. Proxmox is a Debian-based distro which uses such approach (upto 1.9 without any fencing device but only with DRBD+Heartbeat and from 2.0 Proxmox uses DRBD with Corosync. A pretty robust enterprise grade solution. Just for information.
 
My issues thus far with the ZFS + HAST + CARP + DEVD setup are during system startup and shutdown (related forum post is here: http://forums.freebsd.org/showthread.php?t=29996)

Hast1 and hast2 are up, running, and properly replicating. Hast1's role is primary, hast2's role is secondary.

Issue #1


I pull the (power) plug on hast1 to simulate some type of failure.
Hast2 takes over and everything is perfect.
I put hast1 back into service (plug the power back in).
FreeBSD boots up
The CARP interface on hast1 switches to MASTER and hast2 switches to BACKUP
hast2's role is now secondary
hast1's role is stuck at init
storage system is down :(
​

The cause of this issue is fully explained in the related forum post. Basically it has to due with the fact that hastd isn't running yet. I can easily work around this issue by modifying the fail-over script (start hastd if it's not running), but that generates errors/warnings during boot up and is not as elegant as I want it to be.

Issue #2


I attempt a clean reboot or shutdown of hast1
Hast1 hangs
Hast2 never takes over
storage system is down :(
​

Not sure exactly what causes this issue, but it only happens when the role is primary. Some sources online point to a problem with ZFS and HAST. I have been unable to find a work around/fix for this.

Any assistance would be appreciated, and by the way: net.inet.carp.preempt=0 on both hosts.
 
@tuaris

Issue #1

When my primary server comes back online it does not automatically assume a MASTER role in CARP.
I have to manually issue on both nodes:

[CMD=""]#ifconfig carp0 down && ifconfig carp0 up[/CMD]

Only then do they switch roles. This way I avoid split brain issues.

Issue #2

Very strange!
 
gkontos said:
@tuaris

When my primary server comes back online it does not automatically assume a MASTER role in CARP.
Click to expand...

Interesting, when I reboot either server regardless of it's current role, it always assumes the MASTER role in CARP.

For example I have HostA and HostB...

HostA:
Code: 
carp0: flags=49<UP,LOOPBACK,RUNNING> metric 0 mtu 1500
        inet 1.2.3.4 netmask 0xffffff00
        nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
        carp: MASTER vhid 1 advbase 1 advskew 0

HostB:
Code: 
carp0: flags=49<UP,LOOPBACK,RUNNING> metric 0 mtu 1500
        inet 1.2.3.4 netmask 0xffffff00
        nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
        carp: BACKUP vhid 1 advbase 1 advskew 0

I reboot HostB.

HostA:

Code: 
carp0: flags=49<UP,LOOPBACK,RUNNING> metric 0 mtu 1500
        inet 1.2.3.4 netmask 0xffffff00
        nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
        carp: BACKUP vhid 1 advbase 1 advskew 0

HostB:

Code: 
carp0: flags=49<UP,LOOPBACK,RUNNING> metric 0 mtu 1500
        inet 1.2.3.4 netmask 0xffffff00
        nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
        carp: MASTER vhid 1 advbase 1 advskew 0
 
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