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Could you elaborate on the semantics of "cache"? I do understand the mirror keyword, but I know next to nothing about ZFS and don't really get what "cache" mean

Could you elaborate on the semantics of "cache"? I do understand the mirror keyword, but I know next to nothing about ZFS and don't really get what "cache" means, considering bouth your and OPs comment.

justinsaccount 11y ago
You can use a fast disk like an SSD as a 2nd level cache device after ram. So reads will first check the main ram cache first, then the ssd cache disk before finally hitting the underlying storage.
- feld 11y ago
  L2ARC is extremely well documented right in the code https://svnweb.freebsd.org/base/head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c?view=markup#l5587 https://svnweb.freebsd.org/base/head/sys/cddl/contrib/openso...
clord 11y ago
a cache drive is l2arc. Brendan Gregg's post[0] explains it well, but the TLDR is that l2arc is very much like an l2 cache in a cpu. Recent and relevant items are held on a fast drive in case it will be needed in the near future. It is really an L2 cache: L1 is called ARC and is held in dram. If I recall correctly, the extra indexes and tags mean l2arc requires more memory to work efficiently. [0]: https://blogs.oracle.com/brendan/entry/test https://blogs.oracle.com/brendan/entry/test
- semi-extrinsic 11y ago
  When your "medium-sized test server" has 128 GB RAM and half a TB worth of SSDs... in 2008! Damn.