Re: Very low disk performance Highpoint 1820a

From: Scott Long <scottl_at_samsco.org>
Date: Sun, 08 May 2005 08:35:38 -0600
Steven Hartland wrote:
> ---- Original Message ----- From: "Scott Long" <scottl_at_samsco.org>
> 
> 
>> Steven Hartland wrote:
>>
>>> If that where the case it would have been it wouldn't have been
>>> 46Mb/s it would have been 543Mb/s, just tested it for you :P
>>
>>
>> The RR1280 cards are really just software RAID cards.  All of the parity
>> calculations are done by the CPU.  I couldn't find much evidence that
>> the driver has parity routines that are optimized for the CPU, so it's
>> likely doing a very inefficient job at it.
> 
> 
> According to the documentation this is not the case and the XOR
> calcs are done in hardware on the onboard HPT 601.

Maybe I'm confused and we are talking about different cards.

> 
>> Changing MAXPHYS is very dangerous, unfortunately.  The root of the
>> problem is that kernel virtual memory (KVA) gets assigned to each I/O
>> buffer as it passes through the kernel. If we allow too much I/O through
>> at once then we have the very real possibility of exhausting the kernel
>> address space and causing a deadlock and/or panic.  That is why MAXPHYS
>> is set so low.  Your DD test is unlikely to trigger a problem, but try
>> doing a bunch of DD's is parallel and you likely will.
> 
> 
> Thanks for the heads up on this scott I'll do some tests to see that 
> happens.
> N.B. I'm currently using 256K instead of 128K which has the same
> performance increase as using 1M.
> Note: all tests are being done on i386 not AMD64 due to our requirement
> for i386 Linux emulation which it is my understanding is not available when
> running AMD64 FreeBSD.

Linux/i386 emulation works quite well on FreeBSD/amd64 and is getting 
better every day.  There is active development on it at the moment.

Scott
Received on Sun May 08 2005 - 12:36:05 UTC

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