RAID controller cache

D

Daynja

Weaksauce
Joined
Jan 1, 2005
Messages
119
How important is the cache memory on a RAID controller? I see some without any cache and some with a fixed cache and some with memory slots that can be upgraded. My current RAID controller has a slot that I upgraded to its maximum of 256MB. But as I am looking around for newer controllers I see all but the very high end controllers have no cache or a somewhat small fixed cache.

It seems kind of silly that any SATA RAID controller with an upgradeable cache or at least 256MB is at least 4 times as expensive as the one I currently have. I am hesitating to do any upgrade if I must pay more money for something that isn't as good, if only in this one area.

So how important is the cache for speed? What difference does it make?
 
Its all very technical, and im not going to try to get into it here by any means but the simple version is the cache is meant to improve speed for large file copy and always remember that you get what you payfor, typically things that cost more are faster and better and have more features......usually anyway
 
When reads from the array happen, they get stored in memory. When the same read happens again, it gets returned from memory. When writes happen, they get stored in memory initially, then written to disk when the controller's ready. Old stuff gets tossed out of cache. That's about all.

Also look up "write through" and "write back".

I'd recommend an Areca card if you're looking for speed.

 
unhappy_mage said:
I'd recommend an Areca card if you're looking for speed.
Click to expand...
Speed and a hole in my wallet. Those cards look great but do they even sell anything under $500? I guess I just wasn't meant to have more than 600GB. :(
 
a cached controller will usually give some performance boost over the same non cached controller.
Beware of using writeback cache if this is a mission critical system (and if it isnt too!).
A large write back cache can leave a LOT of data unwritten to the hard drive(s) if the machine stops/crashes.
This can hose Windows easily so be sure to have regular backups.
You can certainly lose data too. Using a transaction oriented system (for databases etc) can ensure you know what data is definitely commited correctly.
Alternatively, turn writeback cache off which will sadly lose a lot of the extra performance. Such is life :)
 
Highpoint makes a series that is significantly easier on the wallet (~$250), and nearly as fast in some apps. Those are my recommendation. The 2220/2320 cards do very well in STR if you don't mind the CPU hit, and fairly okay in other tests.

 
I'm wary of highpoint as I bought one of their cheapie raid 5 cards a couple years ago and it was horrible and then stopped working after 2 days. I got a promise SX4000 to replace it and I've been pretty happy with it since, besides the fact that it's parallel ATA. Because of that and that I'd rather use an external enclosure, I've been looking for something different. Nothing really seems to be that much better and even close to my price range.

btw I do have write-back cache on and I just and let it fly. It's not an OS drive and if anything was dropped during a crash it wouldn't be huge.

thanks for all the information guys.
 
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