Date: Sun, 7 Nov 2004 10:00:33 +1030 From: Greg 'groggy' Lehey <grog@FreeBSD.org> To: Julian Elischer <julian@elischer.org> Cc: current@freebsd.org Subject: Re: Gvinum RAID5 performance Message-ID: <20041106233033.GL24507@wantadilla.lemis.com> In-Reply-To: <4186EDD1.8090805@elischer.org> References: <002401c4bf9c$c4fee8e0$0201000a@riker> <p06002002bdab24905ad8@[10.0.1.3]> <1099286568.4185c82881654@picard.newmillennium.net.au> <p06002006bdabc1160a6a@[10.0.1.3]> <4186EDD1.8090805@elischer.org>
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--kaF1vgn83Aa7CiXN Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable [Format recovered--see http://www.lemis.com/email/email-format.html] Long/short syndrome On Monday, 1 November 2004 at 18:15:45 -0800, Julian Elischer wrote: > Brad Knowles wrote: > >> At 4:22 PM +1100 2004-11-01, Alastair D'Silva wrote: >> >>> The offshoot of this is that to ensure data integrity, a >>> background process is run periodically to verify the parity. >> >> That's not the way that RAID-5 is supposed to work, at least not >> the way I understand it. I would be very unhappy if I was using a >> disk storage subsystem that was configured for RAID-5 and then >> found out it was working in this manner. At the very least, I don't >> believe that we could/should do this by default, and adding code to >> perform in this manner seems to me to be unnecessary complexity. > > You need the background task to read the blocks on the parity stripe > because if you only ever get good reads from teh data stripes and > never read the parity stripe you may grow bad sectors there which > you will not detect until you need then and by then its too late. It > need sto be run at a very low priority however so as to not > interfere with production. That's a possibility, but it's not implemented in old Vinum, and I think Lukas has other issues to address right now. Greg -- When replying to this message, please take care not to mutilate the original text. =20 For more information, see http://www.lemis.com/email.html See complete headers for address and phone numbers. --kaF1vgn83Aa7CiXN Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.6 (FreeBSD) iD8DBQFBjV6ZIubykFB6QiMRAq6aAJ9WYjHw2mrgoLduyGIlBsVMT5EdKACeLvOR 8W2gnMsZHwz/8roXvZBReO8= =cBxC -----END PGP SIGNATURE----- --kaF1vgn83Aa7CiXN--
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