Can ZIL be disabled if using hardware RAID?

[embrais]

I am seeing a huge performance boost by tuning Freenas to have ZIL disabled:

Tunables -> = 1 (enabled)

with ZIL enabled getting no better than 100MBs +/- (2 active hosts iSCSI)

with ZIL disabled getting 300MBs+ (2 active hosts iSCSI)

My question, is this dangerous? The kit has dual power (raw and UPS) so the chance of power failure is mitigated and the controller has a battery backup for the writes.

vol0 /mnt/vol0 43.6 GiB (0%) 7.0 TiB 7.0 TiB HEALTHY
(vol0/stripe/da0p2)

The unit has 16 bays currently 8x2TB populated via RAID10 on a 16port 3ware controller (will add second stripe in future for 14TB total) this is a burn test currently

Without ZIL swap usage is 0 (by design with ZIL disabled I believe)

Any input, comments, concerns welcome.



System Information
Hostname nas1
FreeNAS Build FreeNAS-8.0.4-RELEASE-p2-x64 (11367)
Platform Intel(R) Xeon(TM) CPU 2.80GHz (*DUAL)
Memory 8177MB
System Time Sat Jun 9 01:25:23 2012
Uptime 1:25AM up 51 mins, 1 user
Load Average 1.23, 1.01, 0.94
OS Version FreeBSD 8.2-RELEASE-p7

 

[survive]

Hi embrais,

In a word, NO. Bad idea...don't do it.

http://www.solarisinternals.com/wiki/index.php/ZFS_Evil_Tuning_Guide#Disabling_the_ZIL_.28Don.27t.29

If you are seeing such an improvement disabling the ZIL you should look into putting the ZIL onto a separate, dedicated storage device. Go out & get a pair of fast SLC SSD's (they don't have to be big) and put the ZIL on those (in a mirror).

-Will