It depends on a lot of things. For purely sequential access,
read-ahead-cache can help significantly, but it depends on how many segments
are int he cache and how fast you’re sucking data through it. With writes,
cache can be a large improvement, but it becomes neglegible as data becomes
more random, and the “working set” becomes larger than the cache.
I can provide some specific recommendations, but would need to know more
detail about what you’re actually trying to accomplish. If it’s jsut a file
system, that’s predominantly random, with hot spots. If it’s a database,
that’s more of a mix of random and sequential.
ALL of this also depends greatly on the disk technology as well. High
performance RAID systems can sustain >>50,000 IO’s per second (512 byte ea)
if they’re sequential, but somewhat less if they’re 100% random. What RAID
technology is sitting behind the box also has a lot to do with it (example:
RAID 1+0 reads should be about twice as fast as writes, with no cache. With
cache, they’ll be the same until the cache becomes saturated)
There are lots and lots of variables to all of this.
-----Original Message-----
From: xxxxx@lists.osr.com
[mailto:xxxxx@lists.osr.com]On Behalf Of Marty Corbett
Sent: Tuesday, April 25, 2000 10:25 AM
To: NT Developers Interest List
Subject: [ntdev] RE: Read/Write performance to disk drives
Hi Everyone,
I am trying to optimize read/write performance to disk drives. The disk
drive is the initiator of a DMA. The ATA-66 drives that I have
tested work
best when the DMA size is around 512KB. The Raid drives that I
have tested
work best when the DMA size is 2MB or above. Do these numbers(512KB and
2MB) coorespond to the amount of cache memory that is either on the disk
controller, on the disk itself, or a combination? If the numbers do
coorespond to the amount of cache memory is there a way for an
NT4.0 driver
to determine this cache size? Is there a way to tell what size DMA chunck
to use for optimum performance?
Please reply to: xxxxx@iced.com
Marty Corbett
Integrated Computing Engines (ICE)
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