ZFS Data missing in a degraded zfs pool

cmstorm

New Member


Messages: 4

#1
Hi !

This is my first experience with ZFS.

I have created a raidz2 zfs pool with 5 drives, no spares (I know won't happen again). It's a lab server so no critical data.
The pool became degraded after a HD failure. (showing as FAULTED with too many errors).

Result:
  • Some of data I had previously disappeared

I was wondering if:
  • the data should still be available in a degraded mode?
  • If I replace the faulty drive, will it be possible to recover the lost data?

Thanks !
 

usdmatt

Daemon

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#2
I don’t really see running raidz2 without spares as a massive issue. I run several similar systems with no spare. Part of the benefit of raidz2 is that it I still get redundancy after a failure while I sort out a replacement for the failed disk.

If a single drive has failed but the pool is only degraded I wouldn’t expect to see missing data. What does zpool status look like?
 

ralphbsz

Daemon

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#3
In addition to usdmatt's question: What do you mean by "disappeared"? What exactly happens when you try to access or read the data? What shows up in the system log?
 
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cmstorm

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Messages: 4

#4
I don’t really see running raidz2 without spares as a massive issue. I run several similar systems with no spare. Part of the benefit of raidz2 is that it I still get redundancy after a failure while I sort out a replacement for the failed disk.

If a single drive has failed but the pool is only degraded I wouldn’t expect to see missing data. What does zpool status look like?
Code:
state: DEGRADED
status: One or more devices are faulted in response to persistent errors.
        Sufficient replicas exist for the pool to continue functioning in a
        degraded state.
action: Replace the faulted device, or use 'zpool clear' to mark the device
        repaired.

NAME                                          STATE     READ WRITE CKSUM
        storage                                       DEGRADED     0     0     0
          raidz2-0                                    DEGRADED     0     0     0
            ata-1                 ONLINE       0     0     0
            ata-2  ONLINE       0     0     0
            ata-3  ONLINE       0     0     0
            ata-4  ONLINE       0     0     0
            ata-5  FAULTED      0     0     1  too many errors

errors: No known data errors
 
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cmstorm

New Member


Messages: 4

#5
In addition to usdmatt's question: What do you mean by "disappeared"? What exactly happens when you try to access or read the data? What shows up in the system log?
I had a NFS setup to share over the network. One of the shares was intended to host iso's.
example when a do 'zfs list', I can see only a 300MB file I've added recently under that directory.
All the previous iso's are gone ( but somehow it says that 3,21GB is used)

storage/share/iso 3.21G 2.19T 3.21G /storage/share/iso
 

SirDice

Administrator
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#6
I had a NFS setup to share over the network. One of the shares was intended to host iso's.
example when a do 'zfs list', I can see only a 300MB file I've added recently under that directory.
All the previous iso's are gone ( but somehow it says that 3,21GB is used)
I'm betting you've mounted something on top of it. The data is there just "masked" by the extra mount.
 
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cmstorm

New Member


Messages: 4

#8
Yes, either that or the ZFS dataset isn't actually mounted at all.

The pool has 0 errors and should be perfectly intact.
somehow the dataset wasn't mounted anymore.
by mounting manually using 'zfs mount -a -O' the data appeared again yaay !!!!.
but I still don't understand why it did happen.
 
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