On 04/18/18 12:19 AM, Timothy Coalson wrote:
On Sat, Apr 14, 2018 at 1:43 AM, Nikola M <minik...@gmail.com> wrote:
And also there is the question weather Hard disk cache is turned on if ZFS
uses partition and not the whole drive. Previoiusly, Hard disk caching used
to be turned OFF if ZFS is on partition and not on the whole drive, for UFS
compatibility.
Don't know how it is now nor how to explicitlycheck/turn ON Hard disk
caching if ZFS pool uses partition on drive.
previously discussed several times, long ago (though somewhat difficult to
search for):
https://www.mail-archive.com/zfs-discuss@opensolaris.org/msg49099.html
ZFS never disables caches, and I believe they are almost always already
enabled anyway, so you can forget this concern. From what I understand
from reading the list, the only reason zfs has any code that touches disk
cache settings at all is that long ago, Sun shipped some drives with the
cache disabled by default in the firmware. I think if you aren't using old
drives shipped by Sun, this "whole disk" distinction doesn't matter to you
(as long as you don't also use UFS, anyway).
I think (got confirmation on this some years ago), that Opensolaris (and
illumos) preventively disables disk cache on all drives where partitions
are used for ZFS, to avoid possible problem with UFS partitions on same
drive if cache is on, and that is why disk cache is turned off if using
partitions instead of giving the whole disk to ZFS:
So question is for present-day illumos, until then I can presume it is
the same as before for cache/partition thing, so needing more recent
info on this.
Unlike explanation about shipped drives, I got explanation about UFS
getting garbled if disk cache is On and using partitions.
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