Date: Sun, 07 Mar 1999 21:02:00 -0800 From: Ludwig Pummer <ludwigp@bigfoot.com> To: Laurence Berland <stuyman@confusion.net>, Greg Lehey <grog@lemis.com> Cc: freebsd-questions@FreeBSD.ORG Subject: Re: vinum (how to use after creation) Message-ID: <4.1.19990307205103.00a42670@mail-r> In-Reply-To: <36E34FBD.CB05405A@confusion.net> References: <199903071254.MAA02531@franklin.matlink> <4.1.19990307101720.00c13100@mail-r> <19990308143012.M490@lemis.com>
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You didn't need to send your message twice. At 08:19 PM 3/7/99 , Laurence Berland wrote: >Can someone get a little bit more in depth on the different kinds of plexes? > I'm not >quite clear what the differences are. I'll present simplified examples, but they should be enough for you to get the general idea. > concatenated plexes use the complete address space of each subdisk in >turn. That means that the first subdisk has the first X megabytes of the plex, the next subdisk has the next Y megabytes, etc. up to the total size of the plex. > A striped plex conforms to RAID 0. The address space is taken from each >subdisk >in turn in stripes of a specified size. This makes for more even loading in > many cases. If you've got 2 subdisks, then 1 subdisk has half of the plex, and the other had the other half. The data is "interleaved," meaning that that instead of having the first half of the plex on one drive, every other megabyte is on the first drive, and the 'other' every other megabyte is on the second drive. > A RAID 5 plex incorporates error recovery: if each subdisk is located on a >different physical drive, the plex can continue operation even if any single >drive > involved in the plex fails. IIRC, RAID 5 involves striping + parity. For a 3 subdisk configuration, data is striped between the first two subdisks. The subdisk drive holds parity information for every bit contained on the first two subdisks. A '1' bit on the third subdisk means that the corresponding bits on the first two subdisks are the same, and a '0' means that they are different. So, if any one subdisk goes down, it can later be recreated from the other two. I'll let Greg correct any mistakes I've made... --Ludwig Pummer ( ludwigp@bigfoot.com ) ICQ UIN: 692441 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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