raid card + raid array VS scsi card + raid array

LoOoD · December 30, 2020, 4:18pm

We’ve been using a 16bay raid array attached to a poweredge 1850 via non-raid scsi card as a slave. It works great and is the cheapest per GB we could find at the time. We have 5 mysql processes running as slaves on the single box. Its connected via two scsi channels. Each channel sees two 1TB partitions. Then I stripe them with lvm. The raid array itself has 1GB of cache+battery in it.

Would we see a performance increase if we have it attached to a raid card w/ cache+battery? Or would there no difference?

sterin · December 30, 2020, 4:27pm

The way I read your post you are asking if changing a LVM (software RAID) for a hardware RAID (SCSI RAID card) and other hardware the same would make a difference.

I would say that you would probably not notice any real difference in performance. For the main CPU to handle a software RAID is usually very marginal compared to other CPU intensive tasks. So removing that task from the main CPU usually don’t really give you that much. And if you already have the 1GB cache in your 16bay box then you already have a decent amount of cache.

But the main question when you are talking about performance is that you need to figure out how your DB accesses the data on the disks.
Is it mostly read or mostly write?
Is the access mostly sequential or random?
etc.

This access pattern is very important and has drastic impact on if and how you can improve performance on your storage setup.

LoOoD · December 30, 2020, 4:27pm

I would use lvm in either setup.

to use two channels
snapshots

Mainly wondering if switching to a raid card w/ cache+battery would improve performance with the same setup.

sterin · December 30, 2020, 4:27pm

[B]LoOoD wrote on Sat, 02 February 2008 06:43[/B]

Mainly wondering if switching to a raid card w/ cache+battery would improve performance with the same setup.

OK, I'm assuming that you are running Ultra320 SCSI and that means that the SCSI bus should not be a bottleneck.

So IMO the possible gain you would get with the RAID adapter is the extra 1GB of cache and in that case I would suggest you too look at if you couldn’t use the money to by more cache for the 16bay box instead.