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We need to setup a Dell server w/ a PERC controller (I forget the exact models because I don't have access to the datacenter, but I can get that information if vital). I have 8 drives like below:

5 x 1.2 TB 2 x 1 TB 1 x 600 GB

This is going to be a pretty busy MS SQL server and we were thinking of putting those 5 x 1.2 TB drives in a RAID 5 array, installing the OS on a RAID 1 created using the 2 x 1 TB drives and the 600 GB drive to be left there for random stuff that we might put on it. Are there any pros/cons for using this setup? Thanks.

Mugurel
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    Whatever you don't use RAID 5 - it's dangerous and has been advised against being used for over half a decade - I can bore you with the details if you like but essentially if you like having data don't use it - use R1/10 or R6/60 instead - nothing else. – Chopper3 Aug 22 '16 at 12:32
  • I agree that raid5 is not ideal... very dangerous for large disks (higher chance rather than a new inherent problem compared to small disks), and can also fail during rebuild if some error is not detected (so I wouldn't use on small disks either). And also will add that it is very poor for database performance. Use raid1 or 10 for databases. – Peter Aug 22 '16 at 12:37

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Raid 5 implies that you have 1/x space on each disk for parity and the rest for data, where x = the amount of drives (minimal 3) Assuming you know this already, this means that you only have 1 disk fault tolerance. Also Raid 5 suffers immense performance degradation when you need to rebuild a drive. And performance isn't as high as for example a Raid 10 It is also less flexible for new drives in the future then other implementations.

This isn't ideal at all for a busy database imo.

It would be better to use a Raid 10 for this, since it doesn't have that much performance degradation and it usually reaches higher read and write speeds, since there is no need for parity management. Also one drive can fail on the two sides at the same time, and everything will still be working.

Side note; Raid != backup so make sure you do regular backups of your database.

So I would advise you to do it like this

          -------RAID 0------
         |                    |
(2 x 1.2TB in Raid 1) + (2 x 1.2TB in Raid 1)

Then use the 2 x 1TB for OS and 600 for random stuff as you said

Keep the 5th 1.2TB disk as a spare for any errors if they arise

Kevin
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