Date: Mon, 13 Aug 2012 12:00:17 +0300 From: Petri Helenius <petri@helenius.fi> To: "Steven Hartland" <killing@multiplay.co.uk> Cc: freebsd-fs@freebsd.org, Poul-Henning Kamp <phk@phk.freebsd.dk> Subject: Re: zero deleted blocks Message-ID: <8A6340E3-87B4-45EC-B4B2-8E705FE934E8@helenius.fi> In-Reply-To: <66DF83E4BF514482A094F6F61E24752B@multiplay.co.uk> References: <48610.1344847476@critter.freebsd.dk> <66DF83E4BF514482A094F6F61E24752B@multiplay.co.uk>
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Obviously the most elegant way would be for KVM, Xen and VMware to = support TRIM/UNMAP... Pete On Aug 13, 2012, at 11:58 , "Steven Hartland" <killing@multiplay.co.uk> = wrote: > ----- Original Message ----- From: "Poul-Henning Kamp" = <phk@phk.freebsd.dk> >=20 >=20 >>> 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. >=20 > cam da already has this option with the sysctl:- > kern.cam.da.X.delete_method =3D ZERO >=20 > This however requires the underlying SCSI device supports > Write Same (WS10 or WS16) which seems to fairly rare. >=20 > 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. >=20 > If this was done care should be take with regards performance > as this will be significantly slower than the current methods. >=20 > That said if the underlying device "supports" trim / unmap > it could interpret that how it sees fit. >=20 > Regards > Steve >=20 > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > This e.mail is private and confidential between Multiplay (UK) Ltd. = and the person or entity to whom it is addressed. In the event of = misdirection, the recipient is prohibited from using, copying, printing = or otherwise disseminating it or any information contained in it.=20 > In the event of misdirection, illegible or incomplete transmission = please telephone +44 845 868 1337 > or return the E.mail to postmaster@multiplay.co.uk. >=20
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