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Subjectread_ahead_kb defaults to 0 on 2.6.9-55.0.6ELsmp
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Hey there,

First time posting to the list, hopefully I'm following protocol.

We recently began rolling out updates to our RHEL4 hosts, which
updated us to 2.6.9-55.0.6ELsmp.

However, upon reboot, we noticed I/O was being blocked a little more
than usual. Looking into it, we noticed that the block device
readahead was now being set to 0, instead of 8192 as it was with the
previous 2.6.x kernel. (ie: the read_ahead_kb located in /sys/block/
cciss\!c0d1/queue/read_ahead_kb, at least for our systems)

In previous < 2.6 kernels where the readahead was managed by sysctl,
we had a bunch of settings we'd manage ourselves. However, since it's
an ioctl-managed setting now, I was under the impression the kernel
would decide what it should be set at during boot.

Granted, we can always just echo in a value when the host is brought
up, or run blockdev --setra, but we've never had to do this
previously, so I feel like doing that now would just be a band-aid to
the issue.

Is there something with this kernel I should be aware of, or has
anyone noticed anything similar? Tried searching through some
different threads looking for a similar issue, but to no avail.

Thanks in advance for all the help!

My best,

Chet

-----
Chet Nichols III
mail: chet.nichols@gmail.com
aim: chet
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