On 19/12/14 03:01, Lindsay Mathieson wrote:
On Thu, 18 Dec 2014 10:05:20 PM Mark Kirkwood wrote:
The effect of this is *highly* dependent to the SSD make/model. My m550
work vastly better if the journal is a file on a filesystem as opposed
to a partition.
Obviously the Intel S3700/S3500 are a better choice - but the OP has
already purchased Sammy 840's, so I'm trying to suggest options to try
that don't require him to buy new SSDs!
I have 120GB Samsung 840 EVO's with 10GB journal partitions and just gave this
a go.
No real change unfortunately :( using rados bench.
However it does make experimenting with different journal sizes easier.
Pity. If you used xfs you can try tweaking some of the mkfs
options...but I doubt they will make too much difference.
Looking at the data specs for the 840, it does not seem to have any on
board capacitors. If it did you could risk switching off xfs write
barriers...which would probably make a big difference.
You could try switching *off* the write cache (just in case the 840
behaves like my m550's and gets - oddly- 2x faster for sync writes in
that case)! However disabling the write cache may *considerably*
decrease disk lifetime, so if the setting helps in yur case, you'll need
to conduct some experiments to measure by how much the lifetime is gonna
be impacted.
Cheers
Mark
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