Date: Mon, 10 Nov 2003 01:32:16 -0800 From: John-Mark Gurney <gurney_j@efn.org> To: Pawel Jakub Dawidek <nick@garage.freebsd.pl> Cc: Lukas Ertl <l.ertl@univie.ac.at> Subject: Re: geom_mirror implementation Message-ID: <20031110093215.GD64793@funkthat.com> In-Reply-To: <20031110085115.GE84474@garage.freebsd.pl> References: <20031109003617.K626@korben.in.tern> <20031109023041.GA9171@VARK.homeunix.com> <868ympydcx.fsf@borg.borderworlds.dk> <20031109213450.GB13982@VARK.homeunix.com> <20031110085115.GE84474@garage.freebsd.pl>
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Pawel Jakub Dawidek wrote this message on Mon, Nov 10, 2003 at 09:51 +0100:
> I've start some work on more advance RAID implementation wich should
> fit to GEOM just fine. Every RAID level will be a different GEOM class,
> but with one configuration utility. All classes will share as many code as
> possible to be flexible in adding new RAID levels in futher. Strategy
> of choosing disks, failures handle, etc. should be also general. I want to
> provide support for many on-disk metadata formats if it will be possible.
>
> The bad news is that it is only a concept, I've only some initial code
> and project draft. I hope I'll find time to implement this.
I think GEOM aware raid is a good idea, though it'd be cool to be able
to support controllers/drives that have an onboard engine. I've heard
of scsi drives that have an xor engine that can take a block of data,
xor it with the on disk data, write the new data, and pass the xor'd
data to the parity disk.
I've started writing a raid4 style geom module. I've realized that this
is more complex since blocks can come in at any time, and you have to
be careful.
One thing that I wouldn't mind would be the ability to stick a cache
layer between two GEOM modules. Could we do this by tricky use of a
vnode or something? Read caching with a write through cache is a must
if you want decent performance in raid[45] configs.
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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