Number of HDDs recommended for RAID 5 array

[servan$]

I am going to configure the RAID5 array but I have doubt about number of disks used in this setup or array. I didn’t use more than 5 disks (4D+1P) in 9570V. So don’t know how many disks are recommended RAID5 array. Some people where telling me that if I use more than 5 HDDS, it could decrease the performance. Is that true? Can anyone tell me what is the maximum number of HDDs, a RAID5 array can hold or can be installed? RAID5 array is meant for critical application like a database.

[Valdis]

I am not sure about the numbers here. Technically I can say that it completely depends on the capability of the controller. Practically, I can say that you should use many drives per RAID 5 array. The problem is that RAID 5 array tolerate only one drive failure but if 2 drives get fail, then you are cooked. If you have many drives in RAID 5, then you probably have great risk of failure. If you really want to configure the RAID 5, I urge you not more than 7 drives and leave 1 drive as a hot spare.

One more thing is, if you are looking for a very large RAID 5 array, then use multiple smaller RAID 5 arrays or RAID0 across RAID 5.

[HALLBJORN]

There is actually no clear limit on how many disks can be used for RAID 5 array. Due to this we are always worried about RAID 5's relatively poor write performance and several limitations during the maintenance. 7-8 disks are enough for common RAID 5 deployments. I guess majority of RAID 5 deployments using <10 disks. If you are planning for big such as RAID "50", you should probably thing about nested RAID levels.

[@bLERINA@]

The capacity of number of disks on RAID array is depends on the controllers. I know about the Compaq proliant 4500, 5000, and 5500's which can hold 72 physical disks. Other than this In the IBM PC325, limit was 96 disks. So if you are thinking about above 64 disks, then make sure to get the FC or external controllers (SAN).

[Jokull]

In my opinion the RAID 1+0 is far more better than RAID 5 in terms of performance view (especially during rebuilds). You can get much higher reliability. By RAID 1+0, only thing concerned on both drives in a mirror pair flaw taking down the entire array

however, for RAID 5 or RAID 6 you can use as many drive but you have to worry about the quality RAID controllers that support. Other than this you should check about the onboard cache and battery.