On 04/25/11 11:55, Erik Trimble wrote:
On 4/25/2011 8:20 AM, Edward Ned Harvey wrote:
And one more comment: Based on what's below, it seems that the DDT
gets stored on the cache device and also in RAM. Is that correct?
What if you didn't have a cache device? Shouldn't it *always* be in
ram? And doesn't the cache device get wiped every time you reboot?
It seems to me like putting the DDT on the cache device would be
harmful... Is that really how it is?
Nope. The DDT is stored only in one place: cache device if present,
/or/ RAM otherwise (technically, ARC, but that's in RAM). If a cache
device is present, the DDT is stored there, BUT RAM also must store a
basic lookup table for the DDT (yea, I know, a lookup table for a
lookup table).
No, that's not true. The DDT is just like any other ZFS metadata and can
be split over the ARC,
cache device (L2ARC) and the main pool devices. An infrequently
referenced DDT block will get
evicted from the ARC to the L2ARC then evicted from the L2ARC.
Neil.
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