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We are planning to buy two servers which will going to host an SQL database(PostgreSQL). The second server will work as a live replication of the first database server (hot standby). The question I'm having is about the RAID level to chose for the servers.

Initially I was planning to use RAID 10 on both servers from performance point of view, but since we plan to store 20-30Tb of data during 5 years, RAID 10 gets a bit too expensive (especially since we have to buy two machines). And also I was thinking that the redundancy of RAID 10 is not really needed if we have replication anyway.

So now I'm considering having RAID 5 on each of the replicating servers. With this setup even if there is a failure of RAID 5 on one machine, accompanied by another failure during the rebuild I'll still have a working DB machine. My guess is that the system should be quite reliable this way. Do you think that's a reasonable decision ?

PS I don't really want to use RAID6, because of the write penalty of it.

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up vote 3 down vote accepted

I think as long as you're truly replicating all the data and services from one machine to the other, R5 will be just fine unless you hit a performance bottleneck. Just be sure to designate a hot spare.

I would point out though, that when you get to the quantities you're talking about the rebuild speed of a R5 array could get... lengthy, depending on the number of spindles and the load on your controller.

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Also RAID5 for database has same performance as single HDD. And it does not scale with number of drives. –  DukeLion May 21 '12 at 5:15
    
Who told you that? –  SpacemanSpiff May 21 '12 at 12:14
    
I've seen a lot of benchmarks and did some tests myself. IOPS performance of RAID5 array is almost the same to single drive. –  DukeLion May 21 '12 at 12:28
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There are way too many factors to make that broad a statement, imho. –  SpacemanSpiff May 21 '12 at 13:02
    
Ok, may be my English is too bad to express it correctly. I'm speaking about RAID configuration, assuming all other factors: controller cache, disk type and condition, filesystem settings are identical –  DukeLion May 21 '12 at 13:08

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