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Re: [dm-devel] Simulating faulty disk



>mount -t ext3 /dev/sdb /mnt
Copied some data into /mnt
>dmsetup create d0 --table="0 `blockdev --getsize /dev/sdb` delay /dev/sdb 0 500"
device-mapper: reload ioctl failed: Invalid argument
Command failed
>umount /mnt
> dmsetup create d0 --table="0 `blockdev --getsize /dev/sdb` delay /dev/sdb 0 500"
Worked.

Basically, am trying to test how regular userspace commands to read/write files behave when I/O fails. For this, I need to put a file system and then carry on testing.

But as seen from above, dmsetup is failing to create a flakey/delay device when /dev/sdb
has a filesystem on top of it. Is there any workaround ?

Thanks,
Yathi

On 10/21/2011 9:00 AM, Yathindra wrote:
Ok :) Bryn is there a more elaborate document which shows simple examples to work with device mapper. For a newbie like me it would be really helpful.

Thanks,
Yathi

On 10/21/2011 8:56 AM, Bryn M. Reeves wrote:
On 10/21/2011 03:47 PM, Yathindra wrote:
dmsetup create d0 --table="0 `blockdev --getsize /dev/sdb` delay
/dev/sdb 0 500"
dmsetup create f0 --table="0 `blockdev --getsize /dev/mapper/d0` flakey
/dev/mapper/d0 0 9 1"
mkfs -t ext3 /dev/mapper/f0
...
...
ext2fs_mkdir: Attempt to read block from filesystem resulted in short
read while creating root dir

Can we even mount such a device ?

It's a flakey device :)

With that table you'll have a device that is failing write I/Os for 1s in every ten. If that coincides with mkfs trying to write to the device it will create a corrupted file system.

Depending on what you are trying to test you may want to put data on the device first.

Regards,
Bryn.



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