[Ilugc] ssd and linux
- From: rajasuperman@xxxxxxxxx (Raja Subramanian)
- Date: Thu, 17 Mar 2011 23:19:21 +0530
On Thu, Mar 17, 2011 at 5:47 PM, steve <steve at lonetwin.net> wrote:
This is a very interesting approach. Going beyond periodic syncing, one of the
things I've been planning to try out (although never got around doing) is to
setup my dev environment (ie: app server including the db) on a ramdisk, which
is disk backed up as part of a raid to a loopback mounted disk image :) !
...this is something suggested by someone on IRC -- not sure of the practical
benefits, but it sounds like a nice idea.
Clever, but it's a terrible idea in terms of performance. RAID1 assumes
both your disks have similar performance.
The RAID1 driver will ack disk writes only after both disks in the raid
group successfully commit data. So your write performance is still the
same as that of your HDD.
However, if your IO pattern is primarily reads, you should experience
better than HDD performance.
Since your RAM disk is volatile, your RAID1 array will be in degraded
mode on boot up. You need to handle this case manually.
I'll try to get it done this weekend.
Instead of a loopback mount, suggest you use LVM or a raw block device.
That way you minimize the number of layers you need to go through to disk.
Do let us know the outcome. I would love to be proved wrong ;-)
Btw, there are vendors who retail RAM "disk arrays", eg. ramsan.com.
Works really well for apps high performance apps which do not support
memcached.
- Raja
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