On 03/06/2016 07:58 PM, John Stoffel wrote:
Ram> Any one here actually use SSD caches for RAID arrays? Can you
Ram> share your experience and let me know your choice of the type of
Ram> cache methods your tired/used and why you think one is better or
Ram> worse than other? If it is possible, please provide raid
Ram> type/size and ssd size used.
I'm using a pair of 4Tb drives mirrored, and a pair of 512gb SSDs,
also mirrored, along with lvmcache to setup my caching across a couple
of volumes.
I honestly haven't seen huge improvements, but I also haven't had the
time to do any serious testing either. Whcih I should do. I've been
sorta thinking that using the Phoronix testing stuff would be the way
to go.
My SSDs and 4Tb drives are all on an LSI 8-port SATA controller, PCI-E
4x I think. It's an MPT SAS-2 controller. I did this so that my boot
drives are some partitions on the SSDs, and then I use two more
mirrored partitions for the cache.
And this is an NFS server for my home directories, etc.
I didn't use bcache because you can't remove a cache device without
rebooting, or at least bringing a device offline and back online,
which doesn't fit my desires to be able to dynamically add/remove
caches, esp for the testing I've never bothered to do.
John
I do not have lvm, but already have a live (regular) file system. While
I can accept downtime, I cannot accept formatting drives/disks. I simply
do not have the extra space to copy back and forth. That is why I
thought of dmcache. I ran a fio experiment on my ssd (old curial M4) and
I am getting 6K (random) IOPs whereas my raid gives me about 1.5K. I
really do not see much point unless my new SSD puts out some decent
numbers stand alone.
Thanks for sharing the details of your setup.
Ramesh
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