Does dm handle tape devices?

Does dm handle tape devices?

[lemons_terry]

Hi

I need to provide persistent binding / persistent device naming for tape devices in Linux environments.  Does device mapper provide some facility for this, or is DM only for disk devices?

Thanks
tl

Terry Lemons
Backup Platforms Group
EMC² 
where information lives
4400 Computer Drive, MS D239
Westboro MA 01580
Phone: 508 898 7312
Email: Lemons_Terry@emc.com

Re: Does dm handle tape devices?

[Mike Anderson]

lemons_terry@emc.com <lemons_terry@emc.com> wrote:
> Hi
> 
> I need to provide persistent binding / persistent device naming for tape devices in Linux environments.  Does device mapper provide some facility for this, or is DM only for disk devices?
> 

Device mapper is only for block devices.

I saw your similar question on the udev list. Is there some reason that
udev will not provide a id that you can use. If not you can alter the
udev rules (or add your own) to provide a persistent id for your
environment.

-andmike
--
Michael Anderson
andmike@linux.vnet.ibm.com

RE: Does dm handle tape devices?

[lemons_terry]

Hi

Thanks for the reply.  I have a customer who runs three tape-aware
applications in one Linux system.  Two of those applications use device
files (ex., dev/nst0) to access the tape devices, so the persistent
udev-created symbolic links in /dev/tape/by-id and /dev/generic/by-id
will work fine for those applications.

A third application, alas, uses SCSI IDs to refer to the tape devices.
I've been instructed to seek a persistent naming solution for this
application, too, one that (hopefully) won't require modification of the
application.  I started out looking at the QLogic FC HBA's persistence
capability, and saw that it functions at the target level within a
single HBA.  But I found that some vendors don't support this method of
persistence, opting instead to use device mapper.

Hope this is clear.

tl

-----Original Message-----
From: dm-devel-bounces@redhat.com [mailto:dm-devel-bounces@redhat.com]
On Behalf Of Mike Anderson
Sent: Friday, November 02, 2007 3:51 PM
To: device-mapper development
Subject: Re: [dm-devel] Does dm handle tape devices?

lemons_terry@emc.com <lemons_terry@emc.com> wrote:
> Hi
> 
> I need to provide persistent binding / persistent device naming for
tape devices in Linux environments.  Does device mapper provide some
facility for this, or is DM only for disk devices?
> 

Device mapper is only for block devices.

I saw your similar question on the udev list. Is there some reason that
udev will not provide a id that you can use. If not you can alter the
udev rules (or add your own) to provide a persistent id for your
environment.

-andmike
--
Michael Anderson
andmike@linux.vnet.ibm.com

--
dm-devel mailing list
dm-devel@redhat.com
https://www.redhat.com/mailman/listinfo/dm-devel

Re: Does dm handle tape devices?

[Mike Anderson]

lemons_terry@emc.com <lemons_terry@emc.com> wrote:
> A third application, alas, uses SCSI IDs to refer to the tape devices.
> I've been instructed to seek a persistent naming solution for this
> application, too, one that (hopefully) won't require modification of the
> application.  I started out looking at the QLogic FC HBA's persistence
> capability, and saw that it functions at the target level within a
> single HBA.  But I found that some vendors don't support this method of
> persistence, opting instead to use device mapper.
> 

If the "third application" is wanting a I:T:L nexus for some type of
passthrough SG_IO operation I assume someone must provide the device nodes
to the application to open for its operations (config file??).

Since this is not device mapper specific maybe send me a reply offlist and
maybe I can help guide your request back to the proper list for more
discussion.

-andmike
--
Michael Anderson
andmike@linux.vnet.ibm.com

Re: Does dm handle tape devices?

[Phillip Susi]

lemons_terry@emc.com wrote:
> Hi
> 
> Thanks for the reply.  I have a customer who runs three tape-aware
> applications in one Linux system.  Two of those applications use device
> files (ex., dev/nst0) to access the tape devices, so the persistent
> udev-created symbolic links in /dev/tape/by-id and /dev/generic/by-id
> will work fine for those applications.
> 
> A third application, alas, uses SCSI IDs to refer to the tape devices.
> I've been instructed to seek a persistent naming solution for this
> application, too, one that (hopefully) won't require modification of the
> application.  I started out looking at the QLogic FC HBA's persistence
> capability, and saw that it functions at the target level within a
> single HBA.  But I found that some vendors don't support this method of
> persistence, opting instead to use device mapper.
> 
> Hope this is clear.

Device mapper has nothing at all to do with persistent device names. 
Device mapper is a kernel device driver that creates virtual block 
devices with interesting mappings to underlying block devices, such as 
raid.  Device naming is handled by udev.