Date: Tue, 26 Jul 2011 08:20:09 -0700 From: Chuck Swiger <cswiger@mac.com> To: Jerome Herman <jherman@dichotomia.fr> Cc: freebsd-stable@freebsd.org Subject: Re: Making world but no kernel Message-ID: <02D59047-E03A-4259-B52F-5CD6B35E3304@mac.com> In-Reply-To: <4E2ED74B.9000807@dichotomia.fr> References: <4E2E9F24.1040108@dichotomia.fr> <20110726114438.GA86683@icarus.home.lan> <4E2EB814.9040704@dichotomia.fr> <20110726131655.GA88280@icarus.home.lan> <4E2ECE62.4050605@dichotomia.fr> <23BD778B-B9A4-43ED-97C6-4DF2D13F80F2@mac.com> <4E2ED74B.9000807@dichotomia.fr>
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On Jul 26, 2011, at 8:03 AM, Jerome Herman wrote: > On 26/07/2011 16:58, Chuck Swiger wrote: >> On Jul 26, 2011, at 7:25 AM, Jerome Herman wrote: >>> Actually it is Raid 10 of a sort. Three first halves of the three disk concatenated and mirrored on the three second half of the same drives. >> There's a significant problem right there. Not only will that configuration badly degrade the performance of the RAID volume, it also compromises the goal of redundancy which RAID-1 is supposed to provide. >> >> Regards, > > Disk are interweaved, so the performances are quite good (about 160% of a single drive) A six-disk RAID-10 setup ought to provide nearly 600% read performance improvement and 300% of the write performance of a single drive-- real numbers tend to be perhaps 550%/250% or so. > and the redundancy is here. Any single drive can fail, and the other two will be there to provide data. Basically the first plesk is a-b-c, and the second is b-c-a, so everything should be fine. Yes, if you do that you can survive a single disk failure, but the degraded performance is going to suck, and you have no chance of surviving a second disk outage. A six-disk RAID-10 volume can survive up to 3 disks failing (although it has a 20% chance of losing the RAID with a two-disk failure and a 50% chance of losing data if a third disk goes without anyone fixing things). Regards, -- -Chuck
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