L2ARC and ZIL on same SSD?

[Dmitry Morozovsky]

On Mon, 20 May 2013, Josh Beard wrote:

> I have a file server running 9.1-RELEASE with 24 GB of RAM and a 6 TB zpool
> spread across 12 500GB disks in two raidz1 and 2 spares.  This server
> houses hundreds of home directories for end-users and stays pretty busy
> with both read and writes.
> 
> I'm planning to add two SSDs soon (128 GB each) to help performance and was
> planning to mirror them. I was curious if having the L2ARC and ZIL on the
> same disks (mirrored) is okay.  With some searching, I haven't seen any
> "official" word on this.  I've seen some folks say not to and others
> recommend it.  Adding a second set of SSDs isn't desirable, as I'll start
> cutting into my available storage capacity (16 bay system).
> 
> Any advice or experience with this?

Well, no official words, but -- I use the following setup for our new database 
server, very similar to yours (but RAID10-alike as it's database, not generic 
storage):

root at briareus:/usr/local/etc# zpool status
  pool: br
 state: ONLINE
  scan: scrub repaired 0 in 0h0m with 0 errors on Fri Apr 26 15:29:32 2013
config:

        NAME             STATE     READ WRITE CKSUM
        br               ONLINE       0     0     0
          mirror-0       ONLINE       0     0     0
            gpt/br0      ONLINE       0     0     0
            gpt/br4      ONLINE       0     0     0
          mirror-1       ONLINE       0     0     0
            gpt/br1      ONLINE       0     0     0
            gpt/br5      ONLINE       0     0     0
          mirror-2       ONLINE       0     0     0
            gpt/br6      ONLINE       0     0     0
            gpt/br2      ONLINE       0     0     0
          mirror-3       ONLINE       0     0     0
            gpt/br3      ONLINE       0     0     0
            gpt/br7      ONLINE       0     0     0
        logs
          mirror-4       ONLINE       0     0     0
            gpt/br-zil0  ONLINE       0     0     0
            gpt/br-zil1  ONLINE       0     0     0
        cache
          gpt/br-cache0  ONLINE       0     0     0
          gpt/br-cache1  ONLINE       0     0     0

errors: No known data errors
root at briareus:/usr/local/etc# glabel status | egrep 'zil|cache'
                               gpt/br-zil0     N/A  da8p1
                             gpt/br-cache0     N/A  da8p2
                               gpt/br-zil1     N/A  da9p1
                             gpt/br-cache1     N/A  da9p2
root at briareus:/usr/local/etc# gpart show da8 da9
=>       34  234371453  da8  GPT  (111G)
         34       2014       - free -  (1M)
       2048   16777216    1  freebsd-zfs  (8.0G)
   16779264  217591808    2  freebsd-zfs  (103G)
  234371072        415       - free -  (207k)

=>       34  234371453  da9  GPT  (111G)
         34       2014       - free -  (1M)
       2048   16777216    1  freebsd-zfs  (8.0G)
   16779264  217591808    2  freebsd-zfs  (103G)
  234371072        415       - free -  (207k)

... and it's working pretty well, givins us some tens of kIOPs on database 
writes.

-- 
Sincerely,
D.Marck                                     [DM5020, MCK-RIPE, DM3-RIPN]
[ FreeBSD committer:                                 marck at FreeBSD.org ]
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*** Dmitry Morozovsky --- D.Marck --- Wild Woozle --- marck at rinet.ru ***
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