[Gluster-users] iowait - ext4 + ssd journal

Lindsay Mathieson lindsay.mathieson at gmail.com
Mon Nov 3 23:17:02 UTC 2014

I hope I'm not spamming and irritating the list with all this, my
apologies if its all old hat.

I recreated my gluster 2 disk replica store with ext4 using a 5GB SSD
journal for each journal. So far it seems to be a huge improvement.

VM start up's still trigger 5-10% iowait, but I presume that sustained
reads which the cache wouldn't help so much with.

However general operation of 5 VDI windows vm's (Developer machines)
is much improved with wait times averaging round 0-3% and over
responsiveness very good.

Which leads me to my inevitable questions :)

- Journal size. I actually have up to 55GB of SSD spare. Is there any
point in increasing the SSD journal size over 5GB? the ext4 disk is
3TB (Western Digital Red)

- ext4 creation options. Any recommenced options there?

- ext4 mount options. Recommend options? I'm using "noatime,nodiratime"

- Would it be a real bad idea to mount with:
  * write back cache enabled
  * nobarrier

At the moment this is a test system so I can rebuild without issues,
though copying the test VM's takes a few hours.



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