Re: RAID5 question.

how is the disks performance ? is it OK ?

On Thu, 2005-08-04 at 18:13 +0200, djani22@dynamicweb.hu wrote:

Yes, it is there, I know it.
But its only for resync or not? :-)

----- Original Message -----
From: "Raz Ben Jehuda" <redacted>
To: <redacted>
Cc: "David Greaves" <redacted>; <redacted>
Sent: Thursday, August 04, 2005 5:56 PM
Subject: Re: RAID5 question.

quoted

take a look at /proc/sys/dev/raid/speed_limit_max . it is kilobytes if i
recall correctly.

On Thu, 2005-08-04 at 17:45 +0200, djani22@dynamicweb.hu wrote:

quoted

Thanks a lot for you, and Raz!

The raw devices readahead I already set with the hdparm, and
/sys/block/*/queue/read_ahead_kb, but the md device is only changeable

with

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blockdev. :-)
I dont use lvm, because it is too slow for me....

But unfortunately the problem is still here for me. :(
I continue searching the bottleneck...

Thanks!

Janos

----- Original Message -----
From: "David Greaves" <redacted>
To: "Raz Ben Jehuda" <redacted>
Cc: <redacted>; <redacted>
Sent: Thursday, August 04, 2005 4:56 PM
Subject: Re: RAID5 question.

quoted

And notice you can apply different readahead to:
The raw devices (/dev/sda)
The md device (/dev/mdX)
Any lvm device (/dev/lvm_name/lvm_device)

David

Raz Ben Jehuda wrote:

quoted

read the blockdev man page

On Thu, 2005-08-04 at 16:06 +0200, djani22@dynamicweb.hu wrote:

quoted

Hi list, Neil!

I have a little question because I'v got some performance problem...
Is the RAID5 do any type of headahead with the default config?
It is possible to disable the readahead? (if it is.)
Or just the io_sched do that on the disks?

How can I disable the whole headahead on top of the RAID5 array?

The RAID5 can do multiple small (<4kb) reads of disks for the

multithreaded

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read requests?
(chunk size is 32k)

Thanks for helping!

Janos

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