Date: Mon, 13 Aug 2012 09:58:08 +0100 From: "Steven Hartland" <killing@multiplay.co.uk> To: "Konstantin Belousov" <kostikbel@gmail.com>, "Poul-Henning Kamp" <phk@phk.freebsd.dk> Cc: freebsd-fs@freebsd.org, Petri Helenius <petri@helenius.fi> Subject: Re: zero deleted blocks Message-ID: <66DF83E4BF514482A094F6F61E24752B@multiplay.co.uk> References: <48610.1344847476@critter.freebsd.dk>
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----- Original Message -----
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
>>I think TRIM support in UFS can be extended to zero-out the deleted
>>blocks, with relatively small amount of work. Basically, in
>>ufs/ffs/ffs_alloc.c:ffs_blkfree(), a BIO_WRITE of zero buffer shall be
>>issued instead of BIO_DELETE.
>
> It would be a better idea to give geom_disk a per-disk option to
> convert BIO_DELETE to writes of zeros.
cam da already has this option with the sysctl:-
kern.cam.da.X.delete_method = ZERO
This however requires the underlying SCSI device supports
Write Same (WS10 or WS16) which seems to fairly rare.
I'm not aware of any an equivalent ATA command, but it would
be possible to have both use a standard write to achieve that.
If this was done care should be take with regards performance
as this will be significantly slower than the current methods.
That said if the underlying device "supports" trim / unmap
it could interpret that how it sees fit.
Regards
Steve
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