Darren J Moffat wrote:
Erik Trimble wrote:
So SSDs for ZIL/L2ARC don't bring that much when used with
raidz2/raidz3,
if I write a lot, at least, and don't access the cache very much,
according
to some recent posts on this list.
Not true.
Remember: ZIL = write cache
ZIL is NOT a write cache. The ZIL is the Intent Log not a cache. It
is used only for synchronous writes. It is not a cache because the
term "cache" implies the data is also somewhere else and you lose
nothing but potential performance if you loose the cache.
ZFS calls the devices used to hold the ZIL (there is one ZIL per
dataset) a SLOG (Separate Log device).
Note also the recent addition of the "logbias" dataset property.
I should have more properly used the term "buffer", which is what ZIL is
more closely related to. Sorry about that - I didn't mean to imply that
the ZIL was the same as something like a STK6140's NVRAM.
--
Erik Trimble
Java System Support
Mailstop: usca22-123
Phone: x17195
Santa Clara, CA
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