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Date: Tue, 16 Dec 2008 12:35:36 +0000
From: "Bryn M. Reeves" <bmr@redhat.com>
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Subject: Re: [linux-lvm] can I freeze I/O for some time to a given disk /
	md /	dm device?
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Tomasz Chmielewski wrote:
> Is it possible to "freeze I/O" for some time to a given disk / md / dm
> device?
> 
> Say, "freeze I/O" so that userspace waits for any response for 30, 60
> seconds or more?

You can suspend/resume dm devices via the dmsetup command.

> If not, is it possible to reset a link repeatedly, like ATA does when it
> hits certain disk problems? I.e., can I do the below manually?
> 
> ata4.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x2 frozen
> ata4.00: cmd 25/00:08:b8:c2:78/00:00:21:00:00/e0 tag 0 dma 4096 in
>          res 40/00:00:bb:c2:78/40:00:21:00:00/e0 Emask 0x4 (timeout)
> ata4.00: status: { DRDY }
> ata4: hard resetting link

This (or something close to it) should be possible using the SCSI fault
injection framework, a project that uses systemtap for injecting faults
under controlled conditions:

http://sourceforge.net/projects/scsifaultinjtst/
http://lwn.net/Articles/265187/
http://lwn.net/Articles/289932/

Regards,
Bryn.


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