On 02/04/2012 11:01, Jack Wang wrote:
2012/4/2 John Robinson<john.robinson@xxxxxxxxxxxxxxxx>
On 02/04/2012 04:15, Jack Wang wrote:
2012/4/1 John Robinson<john.robinson@xxxxxxxxxxxxxxxx
<mailto:john.robinson@xxxxxxxxxxxxxxxx>>
[...]
This might also be a good application for bcache, FlashCache or
whatever.
Using bcache/flashcache is what I'm considering, does above
configuration option still needed?
[...]
Thanks for reply , I mean using SSD as cache device, and raid5
16*7200rpm disks, is this works for streaming workload above?
I know bcache is try to turn rand write to seqencial write, but most
ssd is not good at RAND write as I know.
I don't know where you got that from; SSDs are absolutely brilliant at
small random writes and reads, hundreds of times better than spinning
hard discs. bcache and flashcache were written specifically to take
advantage of SSDs' high I/Os per second for small (random) reads and writes.
I wouldn't touch RAID5 for anything other than 3 drives; I'd use RAID6
or RAID60 for 4-plus where I didn't need the better small/random write
performance of RAID10. I haven't actually used bcache or flashcache,
which is why I introduced them with "might".
My fantasy configuration in your 16-drive chassis would be 2 6-drive
RAID6s, striped together in RAID0, with an SSD cache over the top built
from two SSDs in RAID10 (or if I was feeling really paranoid, 3 SSDs in
RAID10,n3), with the remaining slot containing a hot spare for the RAID6s.
Cheers,
John.
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