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Go Back   Linux Archive > Redhat > Device-mapper Development

 
 
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Old 03-15-2010, 04:59 AM
Mikulas Patocka
 
Default fix snapshot flaws with 4k sectors

Hi

This is series of 4 patches that fix flaws with 4k sectors and snapshots.
The first flaw is bad iterate devices (it can hurt even with 512-byte
sectors, if the snapshot and origin are at devices with different
limits).

The next two patches just prepare things for the 4th patch. The 4th patch
extends the chunk size test for both the snapshot and the origin --- i.e.
chunk size must be greater than or equal to both snapshot and origin
sector size. Previously, the test was only for the snapshot, thus if you
had origin with large sector and snapshot with small sector, it would fail
copying the small chunk from the origin to the snapshot.

BTW. if anyone wants to test his code with non-512-byte sector devices,
you can use old Seagate U160 SCSI disks (Cheetah XL and before), they can
be reformatted to 512-4096 byte sectors with sg_format command. They are
no longer being manufactured, you can find them at internet auctions. The
current U320 SCSI disks (Cheetah 10K.X or 15K.X) don't support large
sectors, they only support 512-528 byte sector-size.

Mikulas

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Old 03-15-2010, 01:08 PM
Mike Snitzer
 
Default fix snapshot flaws with 4k sectors

On Mon, Mar 15 2010 at 1:59am -0400,
Mikulas Patocka <mpatocka@redhat.com> wrote:

> BTW. if anyone wants to test his code with non-512-byte sector devices,
> you can use old Seagate U160 SCSI disks (Cheetah XL and before), they can
> be reformatted to 512-4096 byte sectors with sg_format command. They are
> no longer being manufactured, you can find them at internet auctions. The
> current U320 SCSI disks (Cheetah 10K.X or 15K.X) don't support large
> sectors, they only support 512-528 byte sector-size.

The scsi_debug modules can also be used to create 4K devices.

This is a software-only test-bed but it is bound by the amount of
available ram.

Mike

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