[OpenIndiana-discuss] Using large (3-4 TB) USB disks for backups

[Reginald Beardsley]

Andrew,

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,
Reg


--------------------------------------------
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
 autodetect).
 
 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).
 
 -- Andrew
 
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