Howto for adding a ZIL and L2ARC on one SSD using the shell

[crowi]

Dear Moderators and Admins,

I am still pretty new to N4F and ZFS but I am learning.

I would like to contribute a little Howto, see subject, because from the beginning I liked the idea to optimize my system and tinker around , that's what I was missing on my previous commercial NAS.

Here's my howto for adding a log/ZIL and a cache / L2ARC to the ZFS Pool, using one SSD for both purposes.
I am indeed aware that it is possibly better to use a mirrored device, at least for ZIL, but this is just one more adjustment if anyone needs to use it.
I am not sure if I made everything correctly, so no warranty from my side, but it worked...


1) Add the SSD to your system (in my case ada6) using the webGUI
2) open a shell
3) partition the drive, first clean the drive

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 gpart destroy -F ada6 

add GPT partition

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gpart create -s GPT ada6

add the ZIL partition in my case 10 GB (from iostat testing, ZIL does not need to be much bigger)

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gpart add -s 10G -t freebsd-zfs ada6 

add the remaing space for the L2ARC partition (in mycase 45G)

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gpart add -s 45G -t freebsd-zfs ada6

check the partitions

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gpart show ada6 

4) now it's time to add the devices to the pool:
add the ZIL (log)

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zpool add Poolname log ada6p1

add the L2ARC (cache)

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zpool add Poolname cache ada6p2

5) done...
6) check the pool, in my case it loks like this now from the webGUI

pool: Pool5x3TB
state: ONLINE
scan: none requested
config:

NAME STATE READ WRITE CKSUM
Pool ONLINE 0 0 0
raidz1-0 ONLINE 0 0 0
ada0 ONLINE 0 0 0
ada1 ONLINE 0 0 0
ada2 ONLINE 0 0 0
ada3 ONLINE 0 0 0
ada4 ONLINE 0 0 0
logs
ada6p1 ONLINE 0 0 0
cache
ada6p2 ONLINE 0 0 0

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zpool list -v

7)lean back and watch iostat juggling with the files, log and cache enjoy !!!
eg:

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zpool iostat -v 2 300

FINAL remarks: do not expect a mindblowing boost of performance, my system works smooth and I feel a slight improvement, as well as iostat shows heavy use of the SSD as well.
Use a fast SSD!
Everything can be removed again without damage, just feel free to try it.



Cheeers,
Crowi

[ku-gew]

Keep in mind that ZFS uses the L2ARC mostly for static files with a random access pattern. If the file is read in a streaming fashion (or a lot of it is read), L2ARC is not used.
In other words, L2ARC it's not a good use of money for home NASes, it makes sense only if you have a SSD lying around or if you have databases and such in a pro environment.
At home, just save the SATA port for a redundancy disk and the money for RAM.

[crowi]

I agree, but this Howto is anyway intended for people who want to try out the different options,
as I was missing this one piece I just wanted to contribute...

Cheers,
Crowi

[RedneckBob]

I agree, but this Howto is anyway intended for people who want to try out the different options,
as I was missing this one piece I just wanted to contribute...

Cheers,
Crowi

Great post, thanks. I just happen to have a 32G SSD drive laying around and while my current box is plenty fast for my needs, I'm going to add the SSD drive just for kicks.

[Lee Sharp]

Actually, I can see this being quite useful. Most very fast SSDs are significantly larger than actually needed for a ZIL device. Making half of them a l2arc will not impact ZIL performance at all other than the I/O contention, which may not even come up that much.

Kudos crowi!

[siftu]

It would be interesting to see your before and after performance figures. We have had users do this only to suffer far worse performance than just raw disk.

[byroncollege]

What about aligning the ZIL for 4k drives/zfs pools?