Running SSD’s in RAID can get very expensive very quickly. A more cost effective solution is to have a disk RAID and use an SSD as a cache. I’m not sure if any of these are production ready but all are worth watching:
- zfs-fuse – supports the ZFS L2ARC feature which can be used to setup an SSD as a cache for a ZFS pool. Checksums SSD data and supports multiple devices.
- bcache – a recent project for caching linux block devices. Currently only supports 1 cache device and offers no checksumming.
- flashcache – created and released by and for facebook this at least seems to be in production. documentation is not great however.
Abandoned Projects:
- devcache – http://code.google.com/p/devcache/
- dmcache – http://visa.cis.fiu.edu/ming/dmcache/
Bcache isn’t production ready, but it’s getting closer 🙂 I should have a beta version up within a week, ought to be suitable for desktop use provided you have backups. More than happy to answer any questions about it.
I am running flashcache on my home server, 60Gb of SSD caching a RAID5 array of 3x2Tb hard disks.
Ubuntu server, 2.6.38-11.
Works well in write-through.
In write back the write-backs never seem to happen, even if I take the maximum dirty seconds parameter right down. Then when I rebooted my machine, kernel panic. Haven’t isolated it further.
Moral : stick to write-through for the moment.