Raid 1 or Raid 5?

Question

Before i start i would like to mention i understand the main differences between the major raid version. With that in mind We are currently running raid 5 on our PE 1600sc (4 HD's). We just purchased a new PE 1800 and i am having a tough time choosing between raid 1 or raid 5.   The 1800 will be used for file server and application server via terminal services. It will not be (under normal conditions) heavily loaded as is pertains to I/O's. The array will need to have better reads then writes, availability is paramount. The 1600 will remain the IIS, ISA, SQL, etc. which i will leave the raid 5 as is.   In a raid 1 array with (4) 80 GB HD's, would you only have 80GB capacity or would you get 160 GB? Could i loose 3 HD's and the array still work? Ive read the array will regen faster in raid 1 then raid 5 typically, which is not critical.   I would normally lean toward raid 5 but am undecided on this new file/app server.   Opinions would be appreciated.   Thanks

willirl · Answer

Raid 1 is simply mirroring one drive to another. So if you have two 80GB drives mirrored, you can store 80GB on that array. This way if one disk fails you can still read the data from the other non-failed disk. This is the simplest and cheapest redundant RAID method.

Assuming matched drives:

Capacity = single drive capacity/2

Raid 5 uses striping and parity with parity being distributed between all of the drives in the array. Requires 3 drives minimum. The biggest advantage with 5 is that the storage efficiency is higher so you can store more data on the same number of drives.

Assuming matched drives:

Capacity = single drive capacity * (number of drives - 1)

Also, because of write speed, you should only use Raid 5 if it is a hardware raid (i.e. the controller board supports it)

Here is a nice discussion of RAID levels:

http://www.pcguide.com/ref/hdd/perf/raid/levels/index.htm

EtaEngs · Answer

I appreciate the post but this is not the answer or opinion i was looking for.   I dont need to know how the different raid levels work. I already know that, i am looking for opinions on which raid level (1, 5, 1+0) i should use. I will have (4) 80 GB hard drives in this array. From what i have been reading, it seems that a raid 1+0 array seems to be my best option. First mirror the set then stripe it.   Also would 4 drives be more more efficient or just as efficient with 2 drives in raid 1?   Again assuming i have (4) 80 GB HD's in raid 1, will i have 80GB of space or 160?   Thanks Message Edited by EtaEngs on 07-21-2005 07:41 AM

willirl · Answer

If you go Mirror, you will have 180GB. You are going to RAID 0 two disks into one virtual disk of 180GB and RAID 0 the other two into another disk of 180GB. Then you'll RAID 1 these two into one virtual disk which will have 180GB.

If you RAID 5 all 4 disks into one virtual disk you'll end up with 80 * (4 - 1) = 240GB (see formula in my post above). I think I'd choose this option.

The URL I gave you in my post above contains a informative discussion of RAID.

Richard

EtaEngs · Answer

I think ive decided to do Raid 10. Ill get the redundancy of raid 1 and the performance of raid 0 (for the most part) plus this array will be able to sustain multiple drive failures unlike raid 5. And from what i understand has better read and writes vs raid 5.

Thanks

PowerEdge HDD/SCSI/RAID

Raid 1 or Raid 5?

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