On 03/13/2012 04:06 AM, Kiran Patil wrote:
Hi,
Is anybody using bcache with SSD instead of battery powered raid cards
with Btrfs ?
Hard drives are cheap and big, SSDs are fast but small and expensive.
Wouldn't it be nice if you could transparently get the advantages of
both? With Bcache, you can have your cake and eat it too.
Bcache is a patch for the Linux kernel to use SSDs to cache other
block devices. It's analogous to L2Arc for ZFS, but Bcache also does
writeback caching, and it's filesystem agnostic. It's designed to be
switched on with a minimum of effort, and to work well without
configuration on any setup. By default it won't cache sequential IO,
just the random reads and writes that SSDs excel at. It's meant to be
suitable for desktops, servers, high end storage arrays, and perhaps
even embedded.
http://bcache.evilpiepirate.org/
Did you ever experiment with this? What results did you find?
There is also something similar called flashcache developed by some
facebook engineer that I'm interested in trying. They are supposedly
using this to speed up mysql+innodb. It is out of mainline tree code
though, and I don't think there is much of an effort to get it in. It
supports writeback, writethrough and writearound (blocks are never
cached on write, only on read) caching. It uses dm-mapper to combine
your 'cache block' with your 'slow spinning block' and then you put your
filesystem on top of that dm device. https://github.com/facebook/flashcache
Regards,
--Justin
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