I am going with a RAID 1 config with 2 36GB 10,000rpm SCSI drives. I have the following choices for primary controllers:

PERC3-DCL RAID Card w/64MB Cache 1 Int/1 Ext Channel
PERC3,DC,128MB,1-INT,1-EXT ($350 more)

My question is will the 128MB cache make a difference from my customers point of view? Is the extra cache worth $350? Has anyone experienced problems with the 64MB cache?

Thanx

Large amounts of cache on RAID controllers only helps significantly when using RAID 5. You may notice 1-2% difference but nothing significant under RAID 1.

Typically the read ahead cache for a RAID controller works best with non-parity arrays and you will get a much better advantage from more read ahead cache. However you really don't need anything more than 32MB for read ahead cache.

Your write cache is going to be very beneficial in every different raid level. The write cache will allow you to buffer your writes to compensate for slow parity algorithms or slow writes to non-striped disks.

I believe that typically the controller is going to use an algorithm to determine how to allocate it's cache memory between read ahead and write which is heavily influenced by whether you use write back or write through. If you're going to be using write back, you will definitely take advantage of a cache over 32MB. Otherwise, 32MB will probably be fine. So even the 64MB should be plenty to start with.

If you do use write back, I would recommend making sure that you get the battery backed cache. Although this shouldn't be a big deal if you have a reliable UPS, it's always nice to have a backup.

Write back just means that the controller tells the computer that the write is complete before it is, because it is in the cache. Write through just means that it tells the truth.