Date: Mon, 14 May 2001 10:48:10 +0930 From: Greg Lehey <grog@lemis.com> To: Dan Phoenix <dphoenix@bravenet.com> Cc: Scott Mace <smace@intt.org>, FreeBSD Questions <questions@FreeBSD.org> Subject: Re: vinum on 2 ide drives? Message-ID: <20010514104810.F88359@wantadilla.lemis.com> In-Reply-To: <Pine.BSO.4.21.0105101443070.10452-100000@gandalf.bravenet.com>; from dphoenix@bravenet.com on Thu, May 10, 2001 at 02:44:40PM -0700 References: <Pine.BSO.4.21.0105101419410.10452-100000@gandalf.bravenet.com> <Pine.BSO.4.21.0105101443070.10452-100000@gandalf.bravenet.com>
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On Thursday, 10 May 2001 at 14:44:40 -0700, Dan Phoenix wrote: > > > 1 concept with vinum i have never understood > is > > drive ibm1 device /dev/ad1s1e > drive ibm2 device /dev/ad2s1e > volume stripe > plex org striped 512b > sd length 58643m drive ibm1 > sd length 58643m drive ibm2 > > > plex org striped 512b > i just stole the 512 from many examples..512 k blocks in my > understanding. Well, no, 512 sectors. > Guess my question is really then when to up it and in what kinda powers. From the man page: org organization [stripesize] Specify the organization of the plex. organization can be one of concat, striped or raid5. For striped and raid5 plexes, the parameter stripesize must be specified, while for concat it must be omitted. For type striped, it specifies the width of each stripe. For type raid5, it specifies the size of a group. A group is a portion of a plex which stores the parity bits all in the same subdisk. It must be a factor of the plex size (in other words, the result of dividing the plex size by the stripe size must be an integer), and it must be a multiple of a disk sector (512 bytes). For optimum performance, stripes should be at least 128 kB in size: anything smaller will result in a significant increase in I/O activ- ity due to mapping of individual requests over multiple disks. The performance improvement due to the increased number of concurrent transfers caused by this mapping will not make up for the performance drop due to the increase in latency. A good guideline for stripe size is between 256 kB and 512 kB. Avoid powers of 2, however: they tend to cause all superblocks to be placed on the first subdisk. A striped plex must have at least two subdisks (otherwise it is a concatenated plex), and each must be the same size. A RAID-5 plex must have at least three subdisks, and each must be the same size. In practice, a RAID-5 plex should have at least 5 subdisks. So why do the simplified commands do 256 kB? When I wrote them, I wasn't aware of this problem. I fixed it in some places, but not in others. I'm doing the rest now. Greg -- Finger grog@lemis.com for PGP public key See complete headers for address and phone numbers To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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