<story><title>How multi-disk failures happen</title><url>http://sysadmin1138.net/mt/blog/2012/12/how-multi-disk-failures-happen.shtml</url></story><parent_chain><item><author>wazoox</author><text>Using RAID-5 is the primary error here. RAID-5 (or single parity RAID of any kind) is &lt;i&gt;obsolete&lt;/i&gt;, period. The story here doesn&apos;t ring true to me to be honest; I&apos;m currently herding several hundred multi-terabytes servers, and multiple drive failures appear in one and only case: when using Seagate Barracuda ES2 1TB or WD desktop class drives. These are the two very problematic setups. In all other cases, use RAID-6 and all will be well.&lt;p&gt;I&apos;d add that current &quot;enhanced format&quot; drives are tremendously better than most older drives. If your drive is a 1 or 2 TB old (512B sectors) drive, use it only for backup or whatever menial use for unimportant data.</text></item></parent_chain><comment><author>gav</author><text>To add some extra emphasis to wazoox&apos;s point, RAID-6 is always a better choice than RAID-5.&lt;p&gt;If you&apos;re willing take a capacity hit for improved write performance, RAID-1+0 is great. Though you can only survive two disks failing if they are in different pairs.&lt;p&gt;You should also not look at RAID as infallible, if the data is important it should be mirrored in multiple locations.</text></comment>
<story><title>How multi-disk failures happen</title><url>http://sysadmin1138.net/mt/blog/2012/12/how-multi-disk-failures-happen.shtml</url></story><parent_chain><item><author>wazoox</author><text>Using RAID-5 is the primary error here. RAID-5 (or single parity RAID of any kind) is &lt;i&gt;obsolete&lt;/i&gt;, period. The story here doesn&apos;t ring true to me to be honest; I&apos;m currently herding several hundred multi-terabytes servers, and multiple drive failures appear in one and only case: when using Seagate Barracuda ES2 1TB or WD desktop class drives. These are the two very problematic setups. In all other cases, use RAID-6 and all will be well.&lt;p&gt;I&apos;d add that current &quot;enhanced format&quot; drives are tremendously better than most older drives. If your drive is a 1 or 2 TB old (512B sectors) drive, use it only for backup or whatever menial use for unimportant data.</text></item></parent_chain><comment><author>Ologn</author><text>Yes.  The decision to use RAID5 instead of RAIDs 1, 10 or 0+1 shows a decision to cut costs.  With mirroring, the mirror drives would take over when a disk failed.&lt;p&gt;Also, only one hot spare is in the set.  Another cost saving.&lt;p&gt;Yet another decision - RAID5 across 7 disks plus a hot spare.  Instead of say across 6 disks or 5 disks.  You have two more chances for a disk to go bust and will have to be rebuilt from parity.&lt;p&gt;What if the disks are OK but the server host adapter card gets fried?  Or the cable between the server and array?  Some disk arrays allow for redundant access to the array, and some OS&apos;s can handle that failover.&lt;p&gt;Before I read the article, I thought it might discuss heat.  Excessive heat is usually the cause when disk arrays start melting down one after another.  Usually the meltdown happens in an on-site server closet/room which was never properly set up for having servers running 24/7.  Usually the straw which breaks the back is a combination of more equipment added, and hot summer days.  Then portable ACs are purchased to temporarily mitigate things, but if their condensation water deposits are not regularly dumped, they stop helping.  This situation occurs more than you would imagine, luckily I have not been the one who had to deal with this for every time I have seen it (although sometimes I have). Usually the servers are non-production ones which don&apos;t make the cut to go into the data center.&lt;p&gt;The heat problem happens in data centers as well, believe it or not.  A cheap thermometer is worth buying if you sense too much heat around your servers.  Usually the heat problem is less bad, but the general data center temperature is a few degrees higher than what it should be, and this leads to more equipment failure.</text></comment>