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On Sun, Apr 10, 2011 at 12:50 AM, Peter Humphrey |
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<peter@××××××××××××××.org> wrote: |
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> On Saturday 09 April 2011 22:01:18 Mark Knecht wrote: |
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> |
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>> Are you running a RAID? |
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> |
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> Yes; mdadm RAID-1, with LVM on top, as in the Gentoo how-to: |
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> http://www.gentoo.org/doc/en/gentoo-x86+raid+lvm2-quickinstall.xml |
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> |
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>> Are you looking for a little redundancy or a lot of redundancy? |
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> |
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> I'm just speculating at the moment, from a dabbler's point of view; what benefits |
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> would accrue from switching from RAID-1 to RAID-5 or above? And, in particular, |
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> what are the comparative virtues of the Samsung disks? |
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> |
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My understanding is there's nothing more reliable than RAID1. mdadm |
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allows N-wide RAID1. My RAID1's are currently 3-drive. |
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Typically the higher RAID numbers are for trading off storage space, |
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redundancy and in some cases throughput. My 5-drive RAID6 gives me |
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(again, my understanding) equivalent redundancy to a 3-drive RAID1. I |
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can lose 2 drives in either RAID before I risk losing everything with |
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a 3rd drive failure, but I only get the storage of 3-drives. A 5-drive |
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RAID5 would lose everything with 2 drive failures but gets 4 drives |
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of storage. |
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As for Samsung drives I have no experience. However one common problem |
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I read about again and again is a RAID user who loses 1 drive and |
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then, while in the process of fixing the RAID, loses a second drive. |
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Most of us (myself included) buy identical drives all at the same time |
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from the same vendor. This means all the drives were likely from the |
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same manufacturing batch and, if they are drives that will fail at all |
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then the group will likely experience multiple drive failures. The |
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underlying idea of RAID is that the drives are not likely to fail at |
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the same time giving us time to fix the array. However, if /dev/sda |
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fails the chances of /dev/sdb failing is higher if they were built at |
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the same time in the same plant. |
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Reading the mdadm list for the last couple of years it seems that many |
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folks running data centers intentionally buy drives from multiple |
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manufactures, or drives of different sizes from the same manufacturer, |
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hoping to lower the chances of multiple failures at the same time. |
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What I did myself was buy 5 drives initially, 3 from Amazon, 2 from |
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NewEgg. For spares I then waited 2 months, bought one more drive, and |
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waited another 2 months and got one more. In my case all my drives are |
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WD RAID Edition drives which have higher reliability specs than the |
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commercial drives. (And are more expensive and smaller) |
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As for hardware RAID the risk I hear about there is that if the |
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controller itself fails then you need an identical backup controller |
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or you risk the possibility that you won't be able to recover |
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anything. I don't know how true that is or whether it's just FUD. |
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Cheers, |
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Mark |
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