On 06/16/11 20:26, Daniel Carosone wrote:
On Thu, Jun 16, 2011 at 09:15:44PM -0400, Edward Ned Harvey wrote:
My personal preference, assuming 4 disks, since the OS is mostly reads and
only a little bit of writes, is to create a 4-way mirrored 100G partition
for the OS, and the remaining 900G of each disk (or whatever) becomes either
a stripe of mirrors or raidz, as appropriate in your case, for the
storagepool.
Is it still the case, as it once was, that allocating anything other
than whole disks as vdevs forces NCQ / write cache off on the drive
(either or both, forget which, guess write cache)?
It was once the case that using a slice as a vdev forced the write cache
off,
but I just tried it and found it wasn't disabled - at least with the
current source.
In fact it looks like we no longer change the setting.
You may want to experiment yourself on your ZFS version (see below for
how the check).
If so, can this be forced back on somehow to regain performance when
known to be safe?
Yes: "format -e"-> select disk -> "cache" -> "write" ->
"display"/"enable"/"disable"
I think the original assumption was that zfs-in-a-partition likely
implied the disk was shared with ufs, rather than another async-safe
pool.
- Correct.
Neil.
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