Re: Very low disk performance Highpoint 1820a

---- 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.

> 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.

    Steve


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