Mar 062016
 

I have recently added two 480 GB SSDs to a 10 x HDD raidz2 system. The SSDs will be mainly used for spooling to tape during backups, but I’m going to use a small part of it for a SLOG. Not all systems benefits from a SLOG (Separate intent LOG), but synchronous writes, such as databases, do. All ZFS systems have a ZIL (ZFS Intent Log); it is usually part of the zpool. Putting the ZIL on a separate device, such as a SSD can boost performance.

Partitioning the drives

My drives are ada1 and ada2.

# gpart create -s gpt ada1
ada1 created

# gpart create -s gpt ada2
ada2 created

# gpart add -t freebsd-zfs -s 8G ada1
ada1p1 added

# gpart add -t freebsd-zfs -s 8G ada2
ada2p1 added

See what that created:

# gpart show ada1 ada2
=>       34  937703021  ada1  GPT  (447G)
         34          6        - free -  (3.0K)
         40   16777216     1  freebsd-zfs  (8.0G)
   16777256  920925799        - free -  (439G)

=>       34  937703021  ada2  GPT  (447G)
         34          6        - free -  (3.0K)
         40   16777216     1  freebsd-zfs  (8.0G)
   16777256  920925799        - free -  (439G)

Creating the log device in the zpool

Let’s create a log device, as a mirror. The zpool we are add it to is system.

# zpool add system log mirror ada1p1 ada2p1

And here is what we have:

# zpool status
  pool: system
 state: ONLINE
  scan: scrub repaired 0 in 38h52m with 0 errors on Fri Mar  4 18:36:22 2016
config:

	NAME        STATE     READ WRITE CKSUM
	system      ONLINE       0     0     0
	  raidz2-0  ONLINE       0     0     0
	    da0p3   ONLINE       0     0     0
	    da1p3   ONLINE       0     0     0
	    da2p3   ONLINE       0     0     0
	    da3p3   ONLINE       0     0     0
	    da4p3   ONLINE       0     0     0
	    da5p3   ONLINE       0     0     0
	    ada0p3  ONLINE       0     0     0
	    da6p3   ONLINE       0     0     0
	    ada3p3  ONLINE       0     0     0
	    da7p3   ONLINE       0     0     0
	logs
	  mirror-1  ONLINE       0     0     0
	    ada1p1  ONLINE       0     0     0
	    ada2p1  ONLINE       0     0     0

errors: No known data errors

All done. Thank you for flying Air FreeBSD.

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