HowTo : Add Log Drives (ZIL) to Zpool

ZIL (ZFS Intent Log) drives can be added to a ZFS pool to speed up the write capabilities of any level of ZFS RAID. It writes the metadata for a file to a very fast SSD drive to increase the write throughput of the system. When the physical spindles have a moment, that data is then flushed to the spinning media and the process starts over. We have observed significant performance increases by adding ZIL drives to our ZFS configuration. One thing to keep in mind is that the ZIL should be mirrored to protect the speed of the ZFS system. If the ZIL is not mirrored, and the drive that is being used as the ZIL drive fails, the system will revert to writing the data directly to the disk, severely hampering performance.

To add a ZIL drive to your ZFS system first run the format command to find the disks that you have available in your system.

Format Command

Once you have run the format command, you should have a list of disks that you can select for your log drives. Select the ones that you would like to use (Our log drives are c4t0d0 and c4t1d0) and issue this command :

zpool add tank log mirror c4t0d0 c4t1d0

Once you issue that command, it should add the log drives to the zpool. Run the “zpool status” command to make sure it was updated as expected.

ZFS Add Log Drives
ZFS Log Drives Added

Thursday, June 3rd, 2010 RAID, ZFS

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