[OpenIndiana-discuss] Using large (3-4 TB) USB disks for backups
pulaskite at yahoo.com
Wed Mar 26 20:19:35 UTC 2014
I got ~24MB/s writing 24 GB to the drive w/o getting a swarm of "copy-modify-write" messages. Just a couple of warnings "block alignment is larger than the pool's alignment". So I think that will work for what I want to do w/ the drive.
I'll see if I can find a disk to try the mirror trick. I think all my other 4k drives are in use though.
Note that I have no problem getting phy_blocksize set properly on the SATA interfaces, it's just for this USB disk that it doesn't get set correctly. I'd have opened the enclosure and used the SATA interface but it is welded plastic. :-(
Thanks for your suggestions,
On Wed, 3/26/14, Andrew Gabriel <illumos at cucumber.demon.co.uk> wrote:
Subject: Re: [OpenIndiana-discuss] Using large (3-4 TB) USB disks for backups
To: openindiana-discuss at openindiana.org
Date: Wednesday, March 26, 2014, 1:35 PM
Have you got any other disk which can
format as ashift=12?
(You could even use an iSCSI LUN from another system with
blocksize set to 4k.)
If so, start by creating a zpool on that. Then attach your
USB drive as a mirror, and it will have ashift=12. Then
detach the original disk from the mirror, and expand the
zpool to fill the whole drive.
Yes, we should have a command line option to set the ashift
given how much trouble the failure to autodetect is causing
in many cases (and you may want to override even a correct
ashift is really a per-top level vdev property rather than a
pool property, and we don't currently have any top level
vdev properties handled by the zpool command.
However, for your usage case of just storing large send
streams, I wouldn't go to any extra bother just to create
ashift=12. There are other situations where it might
actually make a noticeable difference, but I would be
surprised if you see any in this case. You also reduce the
scope for rescue if the pool gets damaged, as ashift=12 has
only 32 previous uberblocks available to work back through
(versus 128 for ashift=9).
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