[bingaling]

Sounds like SSD's are used as a cache, like ZFS does with its l2arc.

[derefr]

For Linux specifically, there are https://github.com/mingzhao/dm-cache and http://bcache.evilpiepirate.org/ as well, which let you use arbitrary filesystems on top. I would bet that Linode is using one or the other of these.

[jevinskie]

Does ZFS use some sort of last-used eviction to purge the cache? It seems like differentiating between random/sequential IO is a bit different than LRU.

[wmf]

The design is documented here: https://github.com/zfsonlinux/zfs/blob/master/module/zfs/arc...