Question about choosing a RAID array

[Preston Aleshire]

Hi all,

  I was wondering if someone might be able to give me some input on choosing a good RAID configuration for our new DL380p server. We have just begun setting it up and are trying to decide between using a RAID 1+0 or a RAID 5 or 6 array. The reason for choosing a RAID 1+0 would be for the performance as well as the ability to continue to operate the array in the event of a drive failure. The downside of a RAID 1+0 for us is that you only achieve half of the capacity of your physical disks.

Choosing RAID 5 would give us more storage space but lower performance. Also, I'm not sure if a RAID 5 array can be used while in a degraded state. Does the array have to be taken offline for a rebuilding to occur? Another question that we have is how much lower the performance is on a RAID 5 array vs. a RAID 1+0 array.

When we booted the server and allowed it to do an automatic configuration of the installed disks, it chose to setup a RAID 6 array.

We are a small business and are going to use this server for multiple things including SQL, SMB shares, and minimal virtual machines. We have 4 600GB SAS 10k HP HDDs installed. Any insight that you can give on which option might be best for us would be greatly appreciated.

Thank you,

 Preston

[Torsten.]

If you have only 4 disks, RAID1 and RAID6 are almost the same in terms of capacity and failure protection. In RAID6 2 disks can fail, in RAID1 every second disk ;-)

However, if a disk in RAID5 fails, the system continues without redundancy until the replaced disks is synced, but you can still work with the array.
With RAID5 you get "1 disk" more space, you have to test if the performance is really lower for your setup.
Finally it is up to you and your needs ... there is probably no single perfect setup for all.

[Preston Aleshire]

Thank you for the insight. I guess I'll have to consider whether or not the abillity to have 2 drive failures is worth the sacrifice of a disk's worth of space.

Thank you again :)

Preston

[Robert_Jewell]

Something else to note is that RAID5 has slightly better write performance than RAID6.  If you setup a spare disk with a RAID5 array you still retain the ability to lose two drives...that is as long as the two drives dont fail at once (the controller needs time to rebuild to the spare).

-Bob

[memeluco]

Hi,

I need some advice about disk space distribution. I'll add 8 900GB disk to a server, using RAID 5 and 1 disk as spare. How many and what size should the logical disk would be?

The server is running Windows 2003 x64 Enterprise Edition.

Thank you in advanced.

[Sarkster]

Hi there,

http://www.raid-calculator.com/default.aspx suggests 5400GB

[memeluco]

Thanks Sarkster , very usefull tool. Now I have another question: according to this tool I will have 5.4TB available, do this means that I'll have to create tree logical disks: 2TB, 2TB and 1.4TB?

Thank you in advanced.