----- Original Message -----
From: "David Greaves" <david@xxxxxxxxxxxx>
To: "Janos Haar" <janos.haar@xxxxxxxxxxxx>
Cc: <linux-raid@xxxxxxxxxxxxxxx>
Sent: Sunday, May 18, 2008 3:00 PM
Subject: Re: questions about softraid limitations
Janos Haar wrote:
The actually best way is this:
blockdev --setro /dev/SOURCE
blockdev --setra 0 /dev/SOURCE
ddrescue -v -b 4096 -B 1024 -e 1 -y 0 /dev/SOURCE /dev/TARGET (if you
dont use a real clean disk with full of zeros, you need the -A option
too)
+ need some kernel patch to disable all retry on the source disk.
Is that something you could share?
Aaa, i made it myself about 1 year before on 2.6.18, but unfortunately at
the moment the source is already deleted, and i dont save the diff. :-(
I am not a good C programmer, but takes about 1 hour. ;-)
It sounds like something that would be worth including in the libata error
handling to be controlled by something like
/sys/block/sdX/device/ioerr_retry_count
This is a great idea! :)
But not just for the ide drives!
I think this is good for all block device!
(usb, scsi, ide, sata...)
Oops.
And an old problem comes again:
On IDE drives with read errors, sometimes drop the DMA.
My script can be re-enable it sometimes, but not the real good solution....
If this can be fixed too, this will be great! :-)
I'd be interested in playing with it and sending to Tejun Heo if you don't
have
time.
The best recovery history is in 3 steps:
[snip]
There is no easy solution. :-(
OK - I'll put this up on the wiki sometime.
Hmm - I wonder if things like ddrescue could work with the md bitmaps
to improve
this situation?
Is this related to David Lethe's recent request?
I think ddrescue is for copy/rescue the data, not for processing it.
But can log the errors... ;-)
Yes - I meant to take the ddrescue output and manipulate the bitmap on the
copied drive to mark certain parts as 'bad'.
Ideally this could be done in the event of a dual-failure so that you
could
re-add 2 failed drives and the bitmaps could indicate.
This may requires something closer to a bytemap but...
This is good in this way. :-)
Cheers,
Janos
David
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