Re: "big" machines running Debian?

["Douglas A. Tutty" <dtutty@vianet.ca>]

On Thu, Feb 26, 2009 at 03:21:44PM -0600, Ron Johnson wrote:
> On 02/26/2009 01:49 PM, Ron Peterson wrote:
> >2009-02-26_14:21:54-0500 "Douglas A. Tutty" <dtutty@vianet.ca>:
> >>On Wed, Feb 25, 2009 at 08:53:45PM -0600, Ron Johnson wrote:
> >>>On 02/25/2009 07:22 PM, Douglas A. Tutty wrote:
> >>>[snip]
> >>>>/proc/megaraid/hba0/raiddrives-0-9 
> >>>>Logical drive: 0:, state: optimal
> >>>>Span depth:  1, RAID level:  1, Stripe size: 64, Row size:  2
> >>>>Read Policy: Adaptive, Write Policy: Write thru, Cache Policy: Cached IO
> >>>>
> >>>>Logical drive: 1:, state: optimal
> >>>>Span depth:  0, RAID level:  0, Stripe size:128, Row size:  0
> >>>>Read Policy: No read ahead, Write Policy: Write thru, Cache Policy: 
> >>>>Cached IO
> >>>Why is Read Ahead disabled on Logical Drive 1?
> >>My understanding is that "read ahead" in this case refers to the ability
> >>of the raid card to read ahead from one disk while a read is taking
> >>place on another disk.  This only makes sense in a redundant raid level.
> >>LD1 is raid0, so there is no other disk from which to read ahead.
> >
> >My understanding is that read ahead means the controller reads more data
> >into memory than you asked for, expecting that the next bits you ask for
> >will be immediately after the ones you just got.
> >
> 
> That *is* the standard definition.  Though there's nothing stopping 
> Megaraid from being weird.

I just checke the setup in the bios and it is set for adaptive
read-ahead on both LDs.  I don't know what's wrong with the output from
/proc.

Doug.