** Changed in: ubuntu-z-systems
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/1860535
Title:
Disable ECKD Thin Provisioning to prevent data loss
Status in Ubuntu on IBM z Systems:
Fix Released
Status in linux package in Ubuntu:
Invalid
Status in linux source package in Eoan:
Fix Released
Bug description:
SRU Justification:
------------------
[Impact]
* A severe problem with 'thin provisioning ECKD volumes', introduced
with 19.10's kernel 5.3, was identified.
* For enhanced space efficient (ese) volumes, errors may occur when
accessing not formatted tracks.
* In such a case the driver either formats the track on the fly for
write requests or returns zero data for read requests.
* But if a write request spans multiple tracks, the indication of an
unformatted track can be in wc applied to all tracks.
* Hence tracks containing data will be handled as empty tracks, resulting in
zero data being returned on read, or overwriting
existing data with zero on write.
[Fix]
* Backport:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1860535/+attachment/5323313/+files/0001-s390
-dasd-disable-ese-support-due-to-possible-data-c.patch
[Test Case]
* An s390x LPAR with Eoan / kernel 5.3 and at least one 3390 DASD
(ECKD) disk is needed ('discard' enabled, which is default).
* Writing arbitrary files (but with known content, e.g. all '1's) to
fill the disk up to a certain level
* Since all 3390 DASDs (mod-3, 9, 27 or 54 ...) have 56,664 bytes per
track, writing a file (again with simple but known content) with a
size of a multiple of 56,664 bytes on a thin provisioned ECKD DASD
device should provoke the error situation.
* Check the files for any modifications (partially filled with '0',
cut/truncated, deleted/zero length).
[Regression Potential]
* The regression potential is moderate since this is purely s390x
specific,
* limited to thin provisioned DASD disks on Eoan / kernel 5.3
* and just disables the broken feature and reverts things back to a
DASD functionality that is known to work.
[Other Info]
* For 19.10 / Eoan no real fix will be provided, but a patch for
disabling this feature completely (this bug/patch).
* The broken functionality that got introduced in Eoan, got already
partially removed due to problems on z/VM.
* For 20.04 / Focal a proper fix is in the works that will be made
available as backport to Focal's kernel 5.4.
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