Red Hat Bugzilla – Bug 503912
library for the Linux Storage Stack
Last modified: 2013-03-05 22:58:26 EST
Description of problem:
Currently, there are no tools/libraries to be able to reliably fiddle with the
Full Storage Stack in Linux (SCSI + "DM - LVM/Multipath" + File System).
For example, I wanted to write a LUN Administration tool. which could be used
to manage the storage stack. Idea was to be able to trigger an
addition/deletion/rescan and see the changes reflected in the entire stack.
Steps required were (example, for deletion):
* Take input from user for the list of LUNs she wants to see deleted. This
could be in the format of the target. Like: lunadm delete -h hostname -l
* The script should then get the LUN ID from the target.
* It should then match the list of relevant SCSI devices.
* It should then see if those devices are in use by DM (Multipath/LVM/Crypt)
* It should see if the DM device is mounted.
* Then, do the trigger.
* Unmount the device.
* Dis-Associate the device from the DM layer.
* Delete the SCSI devices on the host OR simply delete the LUN on the target
and trigger a SCSI rescan on the host.
These steps would reflect the correct changes.
Reasons why I want to do this:
* rescan-scsi is not complete. It'd only rescan the SCSI Bus. Past experiences
have shown stale SCSI device entries. And in many cases, if the LUN goes offline
(with no paths), and you are using DM-Multipath with "queue_if_no_path", you
lose everything. The processes that do a read/write to that device will go
into 'D' state, which till recently not even the kernel was able to kill. Thus
leading you to a System Reset.
* Another reason why I want to use is is because the SCSI + DM stack is not
rigorously tested for LUN addition/deletion. We do claim support for 1000+
devices, but how reliable has it been with frequent 1000 device addition and
deletion. We have applications with that requirement, and they break very
often during addition/deletion of LUNs.
* We'd want to have a library which can be used to cleanly dis-associate and delete a LUN, on request.
*Tomorrow we would have btrfs, which will have many new ideas about blocks, Volumes et cetera.
Anaconda libs, part of the installer, will definitely be implementing those.
* I see the pyblock and pyparted libs to be of great use if you can make them
independent, so that we can write applications on top of a library which will
always be maintained (since anaconda will always use it).
Currently it is very tightly tied to the requirements of anaconda and is not very well documented.
An off-proposal could also be to break the anaconda libs into separate libs to be used by other applications without having a dependency.
Some of the modules I can see are:
partedUtils, partRequests, autopart, dmraid, fsset, iscsi, lvm, partitions
Using libraries that anaconda uses would have many benefits.
* Maintenance (Anaconda uses it. So it sure will be maintained)
bdevid, which is currently a pre-req for pyblock, is packaged as part of mkinitrd. It could be separated.
It looks like you haven't checked out the anaconda storage code in quite a while, as the partedUtils, partRequests, and other python modules within anaconda no longer exists. The pyblock and pyparted rewrites are much more complete, too, and no longer tied so closely to what anaconda wants.
I'm not sure exactly where this bug belongs, but I am positive it's not in anaconda. We could break out our new storage libraries a little bit if there's sufficient interest in making other components work with them. We've been spending some time pushing things into lvm, dmraid, parted, etc. as necessary.
This bug appears to have been reported against 'rawhide' during the Fedora 11 development cycle.
Changing version to '11'.
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