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Description of problem:
We're seeing roughly 20% of the I/Os going to the MDS
when installing a VM over KVM in "none" caching mode (O_DIRECT).
Instrumenting the client revealed that this is caused by buffer
alignment vs. file offset alignment.
Besides being a performance problem, when the MDS caches data
this is also manifested as data corruption when data is written
first via the MDS, then via the DS, eventually the stale data is
read back from the MDS.
Note that this check exists also for the file layout specific
pg_init_* functions.
Version-Release number of selected component (if applicable):
2.6.32-358
How reproducible:
Consistently
Steps to Reproduce:
1. Create a VM with virtio and "none" cachingmode (via RHEV-M or virt-manager)
2. Install VM with RHEL 6.4 from .iso
3.
Actual results:
VM either gets stuck with 100?% cpu util when installing a large package,
or reports the disk is not bootable post installation reboot.
Expected results:
VM installation completes successfully.
Additional info:
That patch not been accepted upstream.... at this point...
Comment 5RHEL Program Management
2013-05-17 12:01:12 UTC
This request was evaluated by Red Hat Product Management for
inclusion in a Red Hat Enterprise Linux release. Product
Management has requested further review of this request by
Red Hat Engineering, for potential inclusion in a Red Hat
Enterprise Linux release for currently deployed products.
This request is not yet committed for inclusion in a release.
Unfortunately not yet. I need to ping Trond about that as we looked into the subject and realized we can implement a layout type specific policy but the ball was dropped.
Comment 8RHEL Program Management
2013-10-14 04:05:58 UTC
This request was not resolved in time for the current release.
Red Hat invites you to ask your support representative to
propose this request, if still desired, for consideration in
the next release of Red Hat Enterprise Linux.