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Subject: Re: Red led dead and disk spindown

Re: Red led dead and disk spindown

From: Mike Holden <>
Date: Wed, 30 Apr 2003 11:06:16 +0100 (BST)

Björn Stenberg said:
> Mike Holden wrote:
>> One of the issues with red led dead is that in some situations, the
>> disk can spin down before the read operation has completed,
> Please elaborate. I've never seen that happen, and the whole purpose of
> last_disk_activity is to prevent this. I don't see how your patch
> changes anything.

You may not have seen it happen, but I have. With appropriate debug
information (I have added some extra WPS elements so I can mointor things
like this) I can conclusively see that the disk spins down before the read
operation has completed. You have admitted yourself that you don't suffer
red dead problem anyway, but I, and many others, do (you are so lucky!).

I appreciate the purpose of last_disk_activity, but we have had a couple
of instances where last_disk_activity has not been updated at the correct
times during disk activity, causing the disk to spindown. We have fixed
these when we have found them. I am convinced that there is at least one
more occasion (maybe more) where this is still happening, despite out best
endeavours. If we can find out where this is, then there is no need for
this patch, but this should sort that particular issue out once and for
all, both now and in the future.

IMHO it is a better solution than having multiple updates of
last_disk_activity scattered throughout the code. At the moment, we only
need to overlook one update, or have an operation last longer than we
expect, and the whole system falls down. This way, we only update it at
the end of the operation, and forcibly lock out the spindown until that
time. A far more elegant solution, again IMHO.
Mike Holden
Received on 2003-04-30

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