2012-06-20 0:32, Timothy Coalson wrote:
when it has 4k sectors, then in theory if "First sector" is a multiple
of 8, it is aligned, but it will probably issue writes of size 512
which will degrade performance anyway).

I think this is dependent on the firmware (vendor), and queued writes
into the same HW sector (4Kb) which came in as a series of 512 byte
blocks should be recombined in HDD cache and written in one stroke.
Thus it should not hurt performance - if write-caching is enabled,
at least, and/or NCQ/TCQ support.

That has its caveats - starting with bug-less-ness of TCQ/NCQ/RMW
and caching, and on into power-failure "support" regarding caches
(i.e. have an UPS or capacitors big enough to flush the disk's
caches safely before parking the heads).

Also by default if you don't give the whole drive to ZFS, its cache
may be disabled upon pool import and you may have to reenable it
manually (if you only actively use this disk for one or more ZFS
pools - which play with caching nicely).

//Jim Klimov
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