ZFS config question using FreeNAS

I have a tower case with a intel 64bit 16GB RAM, but my question is the hardware disk layout

I have two 120GB intel SSD drives and 6 x 3TB Seagate 7200RPM disks.

I want to have the optimum layout for a general NAS server that I can do NFS reads and writes to. Backups, and media storage.

The 3TB drive I was going to ZFS RaidZ2 and mirror the 120GB SSD as logs to improve the writes. The cache I was hoping that the 16GB of RAM would pick up that load.

I was playing with the idea of mirroring the SSDs but doing a split format 1/2 for logs and 1/2 for cache. The thought was that the SSDs could take the load and the mirror would mitigate a SSD drive failure.

I would have loved to have ZFS configured to use a true tier storage where it would auto-move blocks between SSD, and faster and slower HDs (I have old disks) The tower can hold 10 HDs and 4 SSDs

[root@freenas /]# uname -a
FreeBSD freenas.local 8.3-RELEASE-p7 FreeBSD 8.3-RELEASE-p7 #1 r249203M: Sat Apr  6 09:28:27 PDT 2013     root@build.ixsystems.com:/tank/home/jpaetzel/fn8.3/freenas/os-base/amd64/tank/home/jpaetzel/fn8.3/freenas/FreeBSD/src/sys/FREENAS.amd64  amd64
[root@freenas /]# dmesg | grep mem
real memory  = 17179869184 (16384 MB)
avail memory = 16425308160 (15664 MB)
[root@freenas /]# zpool status
  pool: ZFS-Raid-Z2
 state: ONLINE
  scan: none requested
config:

      NAME                                            STATE     READ WRITE CKSUM
      ZFS-Raid-Z2                                     ONLINE       0     0     0
        raidz2-0                                      ONLINE       0     0     0
          gptid/5643058c-1198-11e3-9e5a-d43d7e35d587  ONLINE       0     0     0
          gptid/5699113f-1198-11e3-9e5a-d43d7e35d587  ONLINE       0     0     0
          gptid/571ddcf8-1198-11e3-9e5a-d43d7e35d587  ONLINE       0     0     0
          gptid/57aadd13-1198-11e3-9e5a-d43d7e35d587  ONLINE       0     0     0
      logs
        mirror-1                                      ONLINE       0     0     0
          gptid/57e90a29-1198-11e3-9e5a-d43d7e35d587  ONLINE       0     0     0
          gptid/57fc1f5e-1198-11e3-9e5a-d43d7e35d587  ONLINE       0     0     0

errors: No known data errors
[root@freenas /]#
Brian Sretired geekAsked:
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Daniel HelgenbergerCommented:
I think you may looking for ZFS Hybrid Storage pools (HSP)?
This should in turn be quite easy, using zpool add, please keep in mind some restrictions:
http://www.solarisinternals.com/wiki/index.php/ZFS_Best_Practices_Guide#Separate_Cache_Devices
Also, for RAM caching,
set swapfs_minfree in /etc/system:
http://www.zfsbuild.com/2012/04/18/let-zfs-use-all-of-your-ram/

If you use both, you will have a 3-tier-storage:
1. RAM cache
2. SSD pool
3. SATA disks
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Brian Sretired geekAuthor Commented:
I have rebuilt my ZFS to be:

freeNAS -- Hostname = [freenas.local]
  pool: ZFS-Raid-Z3
 state: ONLINE
  scan: none requested
config:

      NAME                                            STATE     READ WRITE CKSUM
      ZFS-Raid-Z3                                     ONLINE       0     0     0
        raidz3-0                                      ONLINE       0     0     0
          gptid/8c883387-2c25-11e3-b2be-d43d7e35d587  ONLINE       0     0     0
          gptid/8d0787a7-2c25-11e3-b2be-d43d7e35d587  ONLINE       0     0     0
          gptid/8d9706b1-2c25-11e3-b2be-d43d7e35d587  ONLINE       0     0     0
          gptid/8de55100-2c25-11e3-b2be-d43d7e35d587  ONLINE       0     0     0
          gptid/8e550f3e-2c25-11e3-b2be-d43d7e35d587  ONLINE       0     0     0
          gptid/8ee253a0-2c25-11e3-b2be-d43d7e35d587  ONLINE       0     0     0
      logs
        mirror-1                                      ONLINE       0     0     0
          gptid/8f1af888-2c25-11e3-b2be-d43d7e35d587  ONLINE       0     0     0
          gptid/8f31465c-2c25-11e3-b2be-d43d7e35d587  ONLINE       0     0     0
      cache
        gptid/8f481f6d-2c25-11e3-b2be-d43d7e35d587    ONLINE       0     0     0

errors: No known data errors
 
NAME          SIZE  ALLOC   FREE    CAP  DEDUP  HEALTH  ALTROOT
ZFS-Raid-Z3  16.2T   631G  15.6T     3%  1.10x  ONLINE  /mnt
 
 This gives me about 8TB of diskspace since I opted for RaidZ3 -- this I think gives me the best striping and best recovery if a disk fails.

                capacity     operations    bandwidth
pool         alloc   free   read  write   read  write
-----------  -----  -----  -----  -----  -----  -----
ZFS-Raid-Z3   631G  15.6T     12  3.40K  40.8K  58.0M
ZFS-Raid-Z3   631G  15.6T     19  4.48K  28.6K  73.7M
ZFS-Raid-Z3   632G  15.6T     18  3.79K  27.6K  71.2M
ZFS-Raid-Z3   632G  15.6T     21  3.68K  30.0K  60.8M
ZFS-Raid-Z3   632G  15.6T     23  2.96K  34.8K  53.5M

Reads and writes seem to be ok. I see with iostat that the cache disk is being used and the log disk are about 50% of the writes to the disks.

I'm currently moving data back on to the new ZFS FS via find / cpio commands.

My FreeNAS OS does not have a /etc/system file
Reading through the guides I am a bit confused -- the best practices state that I should use entire drives, but other guides should like I can cut it up into slices and then have smaller zvols.
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Brian Sretired geekAuthor Commented:
Sadly ZFS doesn't seem to add any extra value for the tiered storage.
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