Date: Fri, 17 Oct 1997 11:13:47 -0700 (PDT) From: Tom <tom@sdf.com> To: mika ruohotie <bsdhw@shadows.aeon.net> Cc: hardware@freebsd.org Subject: Re: raid Message-ID: <Pine.BSF.3.95q.971017110332.28674A-100000@misery.sdf.com> In-Reply-To: <199710171352.PAA11906@shadows.aeon.net>
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On Fri, 17 Oct 1997, mika ruohotie wrote: > uh, is there documentation exactly how much more disk space one > gains when plugging another drive into raid system. Most RAID systems do not allow you add drives to an existing array. Generally you have to tear down the array setup, and make a new one, losing all previous data. Some can merge in a new drive preserving data, but is time consuming, and array has to be offline. > generally i'm interested in raid5. > > 3 drives is the minimum, right? Yes. > then 4th drive gives the hot spare. how about 5th? 6th? 7th? Not necessarily. You can have anything over 3, not including spares. Generally, 3 or 5 drives is the best choice. Making an array with too many drives will really hurt write performance. > a graph would be nice. There is a simple formula for this that calculate the amount of usable space on any RAID-5 array given the number and size of each drive. For some reason it elludes me now. > what about unstandard raid's (6 7 8 9 10, some of those might not even > exist, but i believe i've seen at least 6 7 and 10) They are non-standard and propietary. Who knows what they do. Generally they are just tweaked RAID-5 type systems, but some sales drone decided to give them a higher number, because bigger is better, and most customers buy into that. > mickey > > Tom
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