Date: Mon, 21 Jan 2013 09:26:30 -0000 From: "Steven Hartland" <killing@multiplay.co.uk> To: "Zaphod Beeblebrox" <zbeeble@gmail.com>, "freebsd-fs" <freebsd-fs@freebsd.org> Subject: Re: ZFS _receiving_ TRIM ? (unmap) Message-ID: <71300B07D20A4B1D900C850AB4450526@multiplay.co.uk> References: <CACpH0MeqtRRD9fPt07Rg2Bw8vVHfeX%2BKTHvVas1Jovc%2BHP8wbw@mail.gmail.com>
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----- Original Message -----
From: "Zaphod Beeblebrox" <zbeeble@gmail.com>
To: "freebsd-fs" <freebsd-fs@freebsd.org>
Sent: Sunday, January 20, 2013 10:45 PM
Subject: ZFS _receiving_ TRIM ? (unmap)
> So... I see that using TRIM is a scheduled feature for ZFS. This is good
> --- ZFS's policy of never overwriting active data make's it's use of TRIM
> all the more important.
>
> But I'm concerned about the other side. If I have an iSCSI disk exported
> from ZFS, will ZFS receive the "UNMAP" (SCSI's TRIM) and free those blocks?
The underlying disk UNMAP / TRIM support is dependent on implementation
at the driver level. For controllers who's driver used cam e.g. scsi (da)
and ata (ada) this is done there.
Having a quick glance at our iSCSI initiator it looks like its based on
cam which means it should work assuming target supports UNMAP or TRIM
via ata_pass. TRIM via ata_pass requires a patch I'm working on here
which works fine on 8.3 but I haven't had chance to port to head or 9/stable
yet.
If you have your setup working with a TRIM compatible ZFS or UFS you can
check the values of kern.cam.da.X.delete_method where X is the disk
number.
If your going to test this ensure you have r239655 in your kernel otherwise
you could get some nasty results.
Regards
Steve
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