Solved GELI + ZFS how much space overhead is normal?

J

jan0sch

Hi,

after creating a zpool on a geli encrypted disk I just noticed:

Code: 
=>
% gpart show da4
        34  7814037100  da4  GPT  (3.6T)
          34           6       - free -  (3.0K)
          40  7813988352    1  freebsd-zfs  (3.6T)
  7813988392       48742       - free -  (24M)

and

Code: 
% zfs list -o space mypool
NAME                      AVAIL   USED  USEDSNAP  USEDDS  USEDREFRESERV  USEDCHILD
mypool                    1.76T   768K        0B     96K             0B       672K

I expected about 10 to 15% overhead but this is half the size. 👀

From the logs I see "GEOM_ELI: gpt/xxx.eli: Failed to authenticate 512 bytes of data at offset 2000381017088"
Which would after my guess be around 1.8 TB.

So could it be that I have to initialise the whole drive with data for geli before I can create the pool?

Kind regards,
 
There shouldn't be any significant overhead.

Can you run a program that prints the size of the eli block device?
 
Output of geli list

Code: 
Geom name: gpt/xxx.eli
State: ACTIVE
EncryptionAlgorithm: AES-XTS
KeyLength: 128
AuthenticationAlgorithm: HMAC/SHA256
Crypto: software
Version: 7
UsedKey: 0
Flags: AUTH, AUTORESIZE
KeysAllocated: 7452
KeysTotal: 7452
Providers:
1. Name: gpt/xxx.eli
   Mediasize: 2000381017600 (1.8T)
   Sectorsize: 512
   Mode: r1w1e0
Consumers:
1. Name: gpt/xxx
   Mediasize: 4000762036224 (3.6T)
   Sectorsize: 512
   Stripesize: 4096
   Stripeoffset: 0
   Mode: r1w1e1

Now this is interesting. 👀
 
Output for an internal drive:

Code: 
Geom name: ada1.eli
State: ACTIVE
EncryptionAlgorithm: AES-XTS
KeyLength: 128
AuthenticationAlgorithm: HMAC/SHA256
Crypto: software
Version: 7
UsedKey: 0
Flags: BOOT, AUTH, AUTORESIZE
KeysAllocated: 3727
KeysTotal: 3727
Providers:
1. Name: ada1.eli
   Mediasize: 1778132381696 (1.6T)
   Sectorsize: 4096
   Mode: r1w1e1
Consumers:
1. Name: ada1
   Mediasize: 2000398934016 (1.8T)
   Sectorsize: 512
   Stripesize: 4096
   Stripeoffset: 0
   Mode: r1w1e1

This looks better and is within the expected overhead range for the HMAC tax. But why is it so far off for the other drive?
 
I tried it with a second drive (also bought recently) and it shows the exact same behaviour.
Also it seems to be related to geli because if I create a zpool without the geli layer then I get the full disk space:

Code: 
NAME        USED  AVAIL  REFER  MOUNTPOINT
mypool      396K  3.51T    96K  none

So far I'm out of ideas. I've created larger geli devices in the past without issue. 🤔
 
jan0sch said:
Output for an internal drive:

This looks better and is within the expected overhead range for the HMAC tax. But why is it so far off for the other drive?
Click to expand...
The difference results from the sector size the "Providers" were initialized with (geli(8) init -s, without specifying the sector size, it defaults to 512):

The 3.6T device was initialized with a "Sectorsize" of 512 , the 1.8T internal device with 4096.

jan0sch said:
Output of geli list
Click to expand...
Rich (BB code): 
Providers:
1. Name: gpt/xxx.eli
   Mediasize: 2000381017600 (1.8T)
   Sectorsize: 512
   Mode: r1w1e0
Consumers:
1. Name: gpt/xxx
   Mediasize: 4000762036224 (3.6T)
   Sectorsize: 512
   Stripesize: 4096
   Stripeoffset: 0
   Mode: r1w1e1

jan0sch said:
Output for an internal drive:
Click to expand...
Rich (BB code): 
Providers:
1. Name: ada1.eli
   Mediasize: 1778132381696 (1.6T)
   Sectorsize: 4096
   Mode: r1w1e1
Consumers:
1. Name: ada1
   Mediasize: 2000398934016 (1.8T)
   Sectorsize: 512
   Stripesize: 4096
   Stripeoffset: 0
   Mode: r1w1e1
 
T-Daemon said:
The difference results from the sector size the "Providers" were initialized with (geli(8) init -s, without specifying the sector size, it defaults to 512):

The 3.6T device was initialized with a "Sectorsize" of 512 , the 1.8T internal device with 4096.
Click to expand...

Thank you very much! That was it!

Code: 
Geom name: gpt/xxx.eli
State: ACTIVE
EncryptionAlgorithm: AES-XTS
KeyLength: 128
AuthenticationAlgorithm: HMAC/SHA256
Crypto: software
Version: 7
UsedKey: 0
Flags: AUTH, AUTORESIZE
KeysAllocated: 7452
KeysTotal: 7452
Providers:
1. Name: gpt/xxx.eli
   Mediasize: 3556232916992 (3.2T)
   Sectorsize: 4096
   Mode: r0w0e0
Consumers:
1. Name: gpt/xxx
   Mediasize: 4000762036224 (3.6T)
   Sectorsize: 512
   Stripesize: 4096
   Stripeoffset: 0
   Mode: r1w1e1
 
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