Stuart Anderson wrote:
On Oct 2, 2009, at 5:05 AM, Robert Milkowski wrote:
Stuart Anderson wrote:
I am wondering if the following idea makes any sense as a way to get
ZFS to cache compressed data in DRAM?
In particular, given a 2-way zvol mirror of highly compressible data
on persistent storage devices, what would go wrong if I dynamically
added a ramdisk as a 3rd mirror device at boot time?
Would ZFS route most (or all) of the reads to the lower latency DRAM
device?
In the case of an un-clean shutdown where there was no opportunity
to actively remove the ramdisk from the pool before shutdown would
there be any problem at boot time when the ramdisk is still
registered but unavailable?
Note, this Gedanken experiment is for highly compressible (~9x)
metadata for a non-ZFS filesystem.
You would only get about 33% of IO's served from ram-disk.
With SVM you are allowed to specify a read policy on sub-mirrors for
just this reason, e.g.,
http://wikis.sun.com/display/BigAdmin/Using+a+SVM+submirror+on+a+ramdisk+to+increase+read+performance
Is there no equivalent in ZFS?
Nope, at least not right now.
--
Robert Milkowski
http://milek.blogspot.com
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