On Tue, November 23, 2010 08:53, taemun wrote:
> zdb -C shows an shift value on each vdev in my pool, I was just wondering
> if it is vdev specific, or pool wide. Google didn't seem to know.
>
> I'm considering a mixed pool with some "advanced format" (4KB sector)
> drives, and some normal 512B sector drives, and was wondering if the
> ashift can be set per vdev, or only per pool. Theoretically, this would
> save me some size on metadata on the 512B sector drives.
It's a per-pool property, and currently hard coded to a value of nine
(i.e., 2^9 = 512). Sun/Oracle are aware of the new, upcoming sector size/s
and some changes have been made in the code:
a. PSARC/2008/769: Multiple disk sector size support
http://arc.opensolaris.org/caselog/PSARC/2008/769/
b. PSARC/2010/296: Add tunable to control RMW for Flash Devices
http://arc.opensolaris.org/caselog/PSARC/2010/296/
(a) appears to have been fixed in snv_118 or so:
http://bugs.opensolaris.org/bugdatabase/view_bug.do?bug_id=6710930
However, at this time, there is no publicly available code that
dynamically determines physical sector size and then adjusts ZFS pools
automatically. Even if there was, most disks don't support the necessary
ATA/SCSI command extensions to report on physical and logical sizes
differences. AFAIK, they all simply report 512 when asked.
If all of your disks will be 4K, you can hack together a solution to take
advantage of that fact:
http://tinyurl.com/25gmy7o
http://www.solarismen.de/archives/5-Solaris-and-the-new-4K-Sector-Disks-e.g.-WDxxEARS-Part-2.html
Hopefully it'll make it into at least Solaris 11, as during the lifetime
of that product there will be even more disks with that property. There's
also the fact that many LUNs from SANs also have alignment issues, though
they tend to be at 64K. (At least that's what VMware and NetApp best
practices state.)
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