On 6/15/2010 11:49 AM, Geoff Nordli wrote:
From: Fco Javier Garcia
Sent: Tuesday, June 15, 2010 11:21 AM
Realistically, I think people are overtly-enamored with dedup as a
feature - I would generally only consider it worth-while in cases
where you get significant savings. And by significant, I'm talking an
order of magnitude space savings. A 2x savings isn't really enough to
counteract the down sides. Especially when even enterprise disk space
is
(relatively) cheap.
I think dedup may have its greatest appeal in VDI environments (think about
a
environment with 85% if the data that the virtual machine needs is into ARC
or
L2ARC... is like a dream...almost instantaneous response... and you can
boot a
new machine in a few seconds)...
Does dedup benefit in the ARC/L2ARC space?
For some reason, I have it in my head that for each time it requests the
block from storage it will copy it into cache; therefore if I had 10 VMs
requesting the same dedup'd block, there will be 10 copies of the same block
in ARC/L2ARC.
Geoff
No, that's not correct. It's the *same* block, regardless of where it
was referenced from. The cached block has no idea where it was
referenced from (that's in the metadata). So, even if I have 10 VMs,
requesting access to 10 different files, if those files have been
dedup-ed, then any "common" (i.e. deduped) blocks will be stored only
once in the ARC/L2ARC.
--
Erik Trimble
Java System Support
Mailstop: usca22-123
Phone: x17195
Santa Clara, CA
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
