can I freeze I/O for some time to a given disk / md / dm device?

can I freeze I/O for some time to a given disk / md / dm device?

[Tomasz Chmielewski]

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?

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


I need this to trace a problem with a userspace application which 
segfaults when ATA resets the link repeatedly (i.e. one broken drive in 
a RAID array).


-- 
Tomasz Chmielewski
http://wpkg.org

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Re: can I freeze I/O for some time to a given disk / md / dm device?

[Gabor Gombas]

On Tue, Dec 16, 2008 at 01:01:27PM +0100, 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?

For real disks you can use /sys/block/sdX/device/unload_heads to achieve
something similar (see Documentation/laptops/disk-shock-protection.txt
in the kernel source about how to use it). That won't work for md/dm
devices though.

Gabor

-- 
     ---------------------------------------------------------
     MTA SZTAKI Computer and Automation Research Institute
                Hungarian Academy of Sciences
     ---------------------------------------------------------

Re: can I freeze I/O for some time to a given disk / md / dm device?

[Tomasz Chmielewski]

Gabor Gombas schrieb:
> On Tue, Dec 16, 2008 at 01:01:27PM +0100, 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?
> 
> For real disks you can use /sys/block/sdX/device/unload_heads to achieve
> something similar (see Documentation/laptops/disk-shock-protection.txt
> in the kernel source about how to use it). That won't work for md/dm
> devices though.

Thanks, I think I have enough hints now.

Bryn M. Reeves on linux-lvm list suggested using dmsetup's 
suspend/resume, which seems to be the easiest way for this purpose 
(requires device mapper / LVM).


-- 
Tomasz Chmielewski
http://wpkg.org