Richard Elling wrote:
Dana H. Myers wrote:
What I do not know yet is exactly how the flash portion of these hybrid
drives is administered. I rather expect that a non-hybrid-aware OS may
not actually exercise the flash storage on these drives by default; or
should I say, the flash storage will only be available to a hybrid-aware
OS.
Samsung describes their hybrid drives as using flash for the boot block
and as a write cache.
-- richard
Here's Seagate's take on the Hybrid HD:
http://www.seagate.com/docs/pdf/marketing/po_momentus_5400_psd.pdf
My understanding of the general design of hybrids is described in the
PDF above: Flash is being used for a READ cache, though I'm not certain
about write caching (whether that too goes through the flash RAM, or
not) - my assumption is that it does NOT, at least in the laptop space.
And, there is no need for OS-level drives - this simply is a plug-in
SATA drive, treated like any other drive. Now, I expect there might be
some optimizations possible should the OS know that the drive is a
Hybrid, but that the drive will still work well (that is, provide better
performance/lower power draw) without any OS modifications.
I do expect that the flash cache will be getting larger (the current
default seems to be 8-16mb, or about the same as a normal RAM cache on a
standard non-hybrid drive), the designers figure out what seems to be a
good mix for the expected environment: that is, I'd estimate that for
the single-drive laptop space, a goodly cache (perhaps enough to cache
the most-common OS libraries, say in the 100MB or so range) is likely,
while the performance market (say for SAS drives), it may be much less
(just enough to keep some frequent metadata around or so).
-Erik
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