Using SSD as disk cache

Question

Is there software for Linux to use an SSD as disk cache? I believe that Sun does something like this with ZFS, though not sure. A quick search provides nothing suitable. The goal would be to put frequently requested files on the SSD on-the-fly. Since the SSD has more capacity than RAM for less money and better performance than hard disk, this should provide an efficient performance boost.

Are you sure SSD is nice for caching? As far as i know, SSD have rewrite limit of about 10000 cycles... — kolypto, Dec 07 '09 at 00:05
Good grief, modern flash SSDs are good for allegedly millions of cycles of writes. See http://serverfault.com/questions/14189/reliability-of-ssd-drives for some further comments. Furthermore, the server will likely be serving up a similar set of files frequently. — casualcoder, Dec 07 '09 at 02:59
See also http://serverfault.com/questions/239808/ssd-for-swap-on-ubuntu-server/239817#239817, which is about swap, but the same caveats apply. — mattdm, Feb 25 '11 at 17:34
Actually it depends. And it isa shame i have to say that in a forum for professionals. There are terrible end user drives out there (25gb, 50gb per day allowed write budget) and thera re high end enterprise drives with 25+ complete rewrites per day(guaranteed over the 5 years you get warranty) and more, which is a LOT of data even for a cache. So, yes, they are adequate if you do not buy total crap cheapo stuff taht is meant for a low use laptop. — TomTom, Apr 25 '14 at 04:27

score 6 · Accepted Answer · answered May 21 '10 at 17:38

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Facebook recently released a module for the Linux kernel called 'FlashCache' which can do exactly this:

http://github.com/facebook/flashcache

answered May 21 '10 at 17:38

user43833

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score 2 · Answer 2 · answered Mar 14 '12 at 20:00

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Have you looked into Bcache? http://bcache.evilpiepirate.org/

I realize this is an old topic, hope this helps anyone else who might have arrived here like me with an ssd cache question.

answered Mar 14 '12 at 20:00

diecast

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score 1 · Answer 3 · edited Jul 26 '12 at 07:28

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With SUN's ZFS, SSDs can be used as L2ARC cache [1], using the zpool add cache command:

cache

A device used to cache storage pool data. A cache device cannot be cannot be configured as a mirror or raidz group. For more information, see the “Cache Devices” section.

I know nothing similar with Linux filesystems. I don't know if it would be suitable, but one thing you may try would be to add swap on SSD and tune the `swapiness' Linux kernel parameter (sysctl vm.swapiness)

edited Jul 26 '12 at 07:28

Lucas Kauffman

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answered Dec 05 '09 at 18:42

zecrazytux

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Swap on SSD won't help file performance - the kernel never uses swap space for page cache... – James Dec 08 '09 at 09:28

score 1 · Answer 4 · answered Dec 05 '09 at 18:49

I don't think there's a simple way to do this on Linux yet. ZFS is available as a userspace filesystem, but it's not very good. Some ZFS clones are on their way, but as far as I know nothing is ready for production.

Perhaps you could consider a BSD with ZFS?

Using SSD as disk cache

4 Answers4