2120S poor performance

Mike Horwath drechsau at Geeks.ORG
Thu Dec 9 09:06:57 PST 2004

On Wed, Dec 08, 2004 at 11:51:21AM -0500, Bill Anderson wrote:
> I've got a 3x72g RAID5 array with U320 disks on an Adaptec 2120S
> controller under Freebsd 4.10.  I'm getting about 25MB/s for sequential
> reads/writes (e.g.  dd if=/dev/aacd0s1b of=/dev/null bs=32k).  I've
> turned on write caching for the container (container set cache
> /write_cache_enable) and turned off the read caching, per previous posts
> to this list.  I'm going to try setting hw.aac.iosize_max to 96k tonight
> to see if that helps.  I'm currently using an IDE disk that gets about
> 45MB/s, so I can hardly consider it an "upgrade" to switch to a 25MB/s
> U320 SCSI system.  :/
> I've also read that the 2120S is slow because of its design.  I'm trying
> to figure out whether the performance can be increased significantly (I
> saw a posting of a linux user getting 37.5MB/s, which although still slow
> might be acceptable), or if I'm better off getting a new card.  I'm
> thinking the latter is the case based on previous postings, but since it
> will probably be quite expensive to replace it, I wanted to get some more
> data.
> What performance should I be expecting from a decent U320 RAID5
> controller?
> Has anyone gotten a 2120S to perform above 30Mb/s in FreeBSD?
> What's the cheapest controller that still gives reasonable performance?
> (If you could give a couple different ones, with their associated
> performance (under FreeBSD), or tell me where to find such information,
> that would be great)

I know I left quite a bit of cruft above, but I don't see these kinds
of performance numbers you are seeing.

First, SCSI does a lot with overlapping I/O and tagged queuing, only
the newest IDE (SATA) systems are starting to support such things.

Second, SCSI disks run at a faster RPM most of the time (only the WD
Raptor hits the 10K mark), lowering seek time significantly.

Third, my numbers:

31MB/sec using

	dd if=/dev/aacd0s1b of=/dev/null bs=32k count=20000

34MB/sec using

	dd if=/dev/aacd0s1b of=/dev/null bs=64k count=20000

33MB/sec using

	dd if=/dev/aacd0s1b of=/dev/null bs=128k count=20000

Now, go and do some testing with random reads and writes and you will
see a big difference between your standard IDE disk and this RAID

The system I was tesing with was loaded down with MySQL operating with
320 tables open, 110 connections, and 128 queries per second,
including one table with 9.7M records and 3.2GB in size.  The system
only has 2GB of RAM.

I use the aac driver for a few of my news feeder boxes, I do primary
storage of my history on a mounted md but I also do all of my other
work via an aac driven RAID5 partition for the things I worry about.
The spool is on an external system and doesn't count :) (the external
system reaches upwards of 70MB/sec using the test above via 1Gbps FC,
and is storaged by WD Raptor SATA 74GB disks).  Each of these boxes
handles 1.4TB of inbound news per day, and each have been doing 2TB
outbound...the RAID systems have been fine...

I also use the amrd driver on my Dell frontend systems for news using
RAID5 and 3x73GB 10K disks, with upwards of 320-450 connections per
server, no issues from the disk subsystems...

Again, random reads and writes are what you might want to worry about,
sequential R/W doesn't happen in a real work environment, at least not
for me.

Mike Horwath, reachable via drechsau at Geeks.ORG

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