Re: *two* RAID arrays better than one?

On 5 May 1998 08:24:54 -0500, rodmant_at_solaria.sol.net (Tom S. Rodman) caused to appear as if it was written:

>We're about to install a new/better hardware RAID card in our
>quad pentium pro HP LXePro Windows NT Server (a 3 channel
>NetRAID card). Should we:
>
> - use our four 9GB drives in a single RAID 5 array
>
> - buy 2 additional 9GB disks and set up 2 separate
> RAID arrays, each with three 9GB disks

The name of the game, when talking about disks, is that the more spindles, the better.

Thus six disks containing data (and, since you are talking about R5, they all will contain data) is better than four.

In addition... a RAID 5 array of N disks can do (N-1)/2 writes simultaneously (best case, etc.). So both a three drive and a four drive array can handle 1 write at a time, while two instances of three drive arrays can handle an aggregate of 2 simultaneous writes.

In addition... (!) Four disks with three SCSI busses dictates that one bus will have two disks on it, which leaves you hoping that if one of those disks chooses to fail, it is polite enough to do so in such a way as to not munge the bus. On the other hand, a pair of three drive sets means that each set will have one drive on each bus; a failed drive might drag down the other unit on the same bus, but it won't result in a loss-of-service event: you'll have two degraded R5 sets.

> Tom Rodman
> Johnson Controls, Inc
Received on Tue May 05 1998 - 00:00:00 CDT