David Magda wrote:
On Jan 2, 2010, at 16:49, Erik Trimble wrote:
My argument is that the OS has a far better view of the whole data
picture, and access to much higher performing caches (i.e.
RAM/registers) than the SSD, so not only can the OS make far better
decisions about the data and how (and how much of) it should be
stored, but it's almost certainly to be able to do so far faster than
any little SSD controller can do.
Though one advantage of doing it with-in the disk is that you're not
using up bus bandwidth. Probably not that big of a deal, but worth
mentioning for completeness / fairness.
This is true. But, also in fairness, this is /already/ being used by
the COW nature of ZFS. Changing one bit in a file causes the /entire/
ZFS block containing that bit to be re-written. So I'm not really using
much (if any) more bus bandwidth by doing the SSD page layout in the OS
rather than in the SSD controller. Remember that I'm highly likely not
to have to read anything from the SSD to do the page rewrite, as the
data I want is already in the L2ARC.
--
Erik Trimble
Java System Support
Mailstop: usca22-123
Phone: x17195
Santa Clara, CA
Timezone: US/Pacific (GMT-0800)
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