Date: Sun, 20 Mar 2005 03:20:05 GMT From: "Greg 'groggy' Lehey" <grog@FreeBSD.org> To: freebsd-bugs@FreeBSD.org Subject: Re: kern/79035: gvinum unable to create a striped set of mirrored sets/plexes Message-ID: <200503200320.j2K3K5l3082072@freefall.freebsd.org>
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The following reply was made to PR kern/79035; it has been noted by GNATS. From: Greg 'groggy' Lehey <grog@FreeBSD.org> To: Sven Willenberger <sven@dmv.com> Cc: freebsd-gnats-submit@FreeBSD.org Subject: Re: kern/79035: gvinum unable to create a striped set of mirrored sets/plexes Date: Sun, 20 Mar 2005 13:41:01 +1030 --RASg3xLB4tUQ4RcS Content-Type: text/plain; charset=us-ascii Content-Disposition: inline [Format recovered--see http://www.lemis.com/email/email-format.html] Single line paragraphs. Please limit your lines to < 80 characters. On Sunday, 20 March 2005 at 2:04:34 +0000, Sven Willenberger wrote: > > Under the current implementation of gvinum it is possible to create > a mirrored set of striped plexes but not a striped set of mirrored > plexes. For purposes of resiliency the latter configuration is > preferred as illustrated by the following example: > > Use 6 disks to create one of 2 different scenarios. > > 1) Using the current abilities of gvinum create 2 striped sets using > 3 disks each: A1 A2 A3 and B1 B2 B3 then create a mirror of those 2 > sets such that A(123) mirrors B(123). In this situation if any drive > in Set A fails, one still has a working set with Set B. If any drive > now fails in Set B, the system is shot. No, this is not correct. The plex ("set") only fails when all drives in it fail. > 2) Using the proposed added ability to create 3 mirror sets A1 and > B1, A2 and B2, A3 and B3. Now create a stripe set across all three > mirrors. Now we can have a situation where one of the "A" drives > fail (for example A1). Then we can also have one of the "B" drives > fail and, as long as it is not "B1" in this case, we still have a > functioning array. Agreed. So there's no difference. > Thus the striping of mirrors (rather than a mirror of striped sets) > is a more resilient and fault-tolerant setup of a multi-disk array. No, you're misunderstanding the current implementation. This is a change request, so I'm not closing (or even assigning to myself) the PR. Greg -- When replying to this message, please take care not to mutilate the original text. For more information, see http://www.lemis.com/email.html Finger grog@FreeBSD.org for PGP public key. See complete headers for address and phone numbers. --RASg3xLB4tUQ4RcS Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.6 (FreeBSD) iD8DBQFCPOnFIubykFB6QiMRAm1BAJsGIfr1v4ILlB4CNBP1t/o67WxYWACePZXj tN2nu75BDBDu5SoDMGB+0BI= =UiI5 -----END PGP SIGNATURE----- --RASg3xLB4tUQ4RcS--
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