RAID 5 vs RAID 10

clifford_m71 used Ask the Experts™
I just want to be sure I understand the difference between RAID 5 and RAID 10. I have a server where my main concern is to increase storage. I have 6 drive slots available to me. I am going to replace the current drives with 6 1TB disks. If I use RAID 5 I will have a logical 4TB disk with 1 hotswap and 1 parity disk. If I use RAID 10 the most I would get out of these drives is 2TB (3 mirrored drives). I know RAID 10 allows for better performance but is there any way to increase that capacity?
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With RAID 10 you would have 3TB available.

The only way you would have 2TB is if you keep 2 HDDs as spares.

Top Expert 2010

The answer is probably moot, because unless you have a UEFI BIOS then the largest device you will be able to boot is 2TB.  

So what you want to do is create a 2 x 1 TB drive pair as a RAID1 for the O/S.   Then take the 4 remaining drives and make it a RAID10.   If you have 2 more slots then many RAID controllers will allow you to resilver the 4-disk RAID10 into a 6-disk RAID10, but you need the bays.

Exactly what controller do you have, what is your O/S, and please check the manual for your computer and see if it can boot a disk > 2TB before you even worry about building a 6-drive RAID5.
Lee IngallsDirector of IT/TS, Quality and Finance
Actually the RAID 1+0 would give you 3TB of mirrored and striped drives. If the added cost isn't  a show stopper I would take the fault tolerance and performance benefits of RAID 10 over RAID 5.
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RAID 5 is poor for writes, but good for reads. 6 1TB disks will indeed give you 4 TB less true capacity overhead so more like 3.72 TB.

RAID 10 is good for both reads and writes. 6 1TB disks will give you 3 TB less true capacity overhead so more like 2.79 TB. RAID 10 can loose UPTO 50% of disks in the array before data loss, so you would be ok with a cold standby disk.
I think I get the confusion.
Raid 10 first creates the stripe on half the drives, then mirrors on the rest.
This way there is no theoretical limit on the number of member HDD's, apart from being at least 4 and even.

So, in the case of 6 HDD's, the controller would create a 3HDD's RAID 0 stripe and then mirror that.

Hope I was clear enough.

clifford_m71IT Manager


The bay that these disks are in actually has 8 slots. Two are RAID1 for the OS already. I am not touching that. So the remaining 6 were what was in question. While I lose 1TB of storage going with RAID10 I think I am better off with the performance. Thanks for the quick refresher course.

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