Hi,
I've been looking for an answer to this question and can't find anything concrete that says full support for write barriers has been backported to the stock kernel.
I've read that:
"There is incomplete write barrier support in kernel versions 2.6.32 and earlier (2.6.31 has some support, while 2.6.33 works for all types of device target) - RHEL 6 uses 2.6.32."
Now, I understand that Red Hat (and therefore CentOS) backport many upstream features into the stock kernel so how can I be sure that kernel 2.6.32-431.11.2.el6 has write barrier support?
Any clues, anyone?
Kind regards, Tom
On 2014-04-01, Tom Robinson tom.robinson@motec.com.au wrote:
Now, I understand that Red Hat (and therefore CentOS) backport many upstr= eam features into the stock kernel so how can I be sure that kernel 2.6.32-431.11.2.el6 has write bar= rier support?
I believe you can look through the RHEL tech notes. Here they are for 6.5:
https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/...
If you require barriers, you can always use the mainline kernel from elrepo. You can read about the mainline and long-term packages here:
http://elrepo.org/tiki/kernel-lt
You probably want the kernel-ml packages, but that page doesn't mention the -lt packages. Lots of CentOS admins use these kernels (including me) and are happy with them.
--keith
On 01/04/14 14:27, Keith Keller wrote:
On 2014-04-01, Tom Robinson tom.robinson@motec.com.au wrote:
Now, I understand that Red Hat (and therefore CentOS) backport many upstr= eam features into the stock kernel so how can I be sure that kernel 2.6.32-431.11.2.el6 has write bar= rier support?
I believe you can look through the RHEL tech notes. Here they are for 6.5:
https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/...
If you require barriers, you can always use the mainline kernel from elrepo. You can read about the mainline and long-term packages here:
http://elrepo.org/tiki/kernel-lt
You probably want the kernel-ml packages, but that page doesn't mention the -lt packages. Lots of CentOS admins use these kernels (including me) and are happy with them.
Thanks Keith.
I took a look at the RHEL tech notes but nothing obvious springs out of that regarding LVM barriers. I wouldn't have imagined it would be so hard to find and answer to this question.
I may go to the elrepo kernels but I'm always hesitant when it comes to changing the core of the system.
Anyone else care to comment or have a clue about LVM barriers in the current kernel?
On 04/01/2014 06:27 AM, Keith Keller wrote:
On 2014-04-01, Tom Robinson tom.robinson@motec.com.au wrote:
Now, I understand that Red Hat (and therefore CentOS) backport many upstr= eam features into the stock kernel so how can I be sure that kernel 2.6.32-431.11.2.el6 has write bar= rier support?
Take a look here: https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/...
Regards, Lec
I believe you can look through the RHEL tech notes. Here they are for 6.5:
https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/...
If you require barriers, you can always use the mainline kernel from elrepo. You can read about the mainline and long-term packages here:
http://elrepo.org/tiki/kernel-lt
You probably want the kernel-ml packages, but that page doesn't mention the -lt packages. Lots of CentOS admins use these kernels (including me) and are happy with them.
--keith
On 01/04/14 17:49, Alexandru Chiscan wrote:
On 04/01/2014 06:27 AM, Keith Keller wrote:
On 2014-04-01, Tom Robinson tom.robinson@motec.com.au wrote:
Now, I understand that Red Hat (and therefore CentOS) backport many upstr= eam features into the stock kernel so how can I be sure that kernel 2.6.32-431.11.2.el6 has write bar= rier support?
Take a look here: https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/...
Regards, Lec
Thanks Lec, I did read this already. It does address filesystems but not LVM. Are write barriers enabled for LVM? Write barriers need to be implemented through the entire stack for them to work. If you have ext4 on LVM on MD not having them on LVM would break the chain. N'est-ce pas?
I believe you can look through the RHEL tech notes. Here they are for 6.5:
https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/...
If you require barriers, you can always use the mainline kernel from elrepo. You can read about the mainline and long-term packages here:
http://elrepo.org/tiki/kernel-lt
You probably want the kernel-ml packages, but that page doesn't mention the -lt packages. Lots of CentOS admins use these kernels (including me) and are happy with them.
--keith
On 04/02/2014 01:00 AM, Tom Robinson wrote:
On 01/04/14 17:49, Alexandru Chiscan wrote:
On 04/01/2014 06:27 AM, Keith Keller wrote:
On 2014-04-01, Tom Robinson tom.robinson@motec.com.au wrote:
Now, I understand that Red Hat (and therefore CentOS) backport many upstr= eam features into the stock kernel so how can I be sure that kernel 2.6.32-431.11.2.el6 has write bar= rier support?
Take a look here: https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/...
Regards, Lec
Thanks Lec, I did read this already. It does address filesystems but not LVM. Are write barriers enabled for LVM? Write barriers need to be implemented through the entire stack for them to work. If you have ext4 on LVM on MD not having them on LVM would break the chain. N'est-ce pas?
from the kernel changelog (https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11...) the barrier support for filesystems, lvm (dm) and md is active from 2.6.32-82-el6
-[fs]jbd2: replace barriers with explicit flush and FUA usage https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/fs-jbd2-replace-barriers-with-explicit-flush-and-FUA-usage.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[fs]jbd2: Modify ASYNC_COMMIT code to not rely on queue draining on barrier https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/fs-jbd2-Modify-ASYNC_COMMIT-code-to-not-rely-on-queue-draining-on-barrier.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[fs]jbd: replace barriers with explicit flush and FUA usage https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/fs-jbd-replace-barriers-with-explicit-flush-and-FUA-usage.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[fs]gfs2: replace barriers with explicit flush and FUA usage https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/fs-gfs2-replace-barriers-with-explicit-flush-and-FUA-usage.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[fs]btrfs: replace barriers with explicit flush and FUA usage https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/fs-btrfs-replace-barriers-with-explicit-flush-and-FUA-usage.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[fs]xfs: replace barriers with explicit flush and FUA usage https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/fs-xfs-replace-barriers-with-explicit-flush-and-FUA-usage.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]pass gfp_mask and flags to sb_issue_discard https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-pass-gfp_mask-and-flags-to-sb_issue_discard.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]disallow FS recursion from sb_issue_discard allocation https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-disallow-FS-recursion-from-sb_issue_discard-allocation.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[dm]convey that all flushes are processed as empty https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/dm-convey-that-all-flushes-are-processed-as-empty.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[dm]fix locking context in queue_io() https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/dm-fix-locking-context-in-queue_io.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[dm]relax ordering of bio-based flush implementation https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/dm-relax-ordering-of-bio-based-flush-implementation.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[dm]implement REQ_FLUSH/FUA support for request-based dm https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/dm-implement-REQ_FLUSH-FUA-support-for-request-based-dm.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[dm]implement REQ_FLUSH/FUA support for bio-based dm https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/dm-implement-REQ_FLUSH-FUA-support-for-bio-based-dm.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]make __blk_rq_prep_clone() copy most command flags https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-make-__blk_rq_prep_clone-copy-most-command-flags.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[md]implment REQ_FLUSH/FUA support https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/md-implment-REQ_FLUSH-FUA-support.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[virt]virtio_blk: drop REQ_HARDBARRIER support https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/virt-virtio_blk-drop-REQ_HARDBARRIER-support.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]loop: implement REQ_FLUSH/FUA support https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-loop-implement-REQ_FLUSH-FUA-support.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]use REQ_FLUSH in blkdev_issue_flush() https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-use-REQ_FLUSH-in-blkdev_issue_flush.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]update documentation for REQ_FLUSH / REQ_FUA https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-update-documentation-for-REQ_FLUSH-REQ_FUA.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]make sure FSEQ_DATA request has the same rq_disk as the original https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-make-sure-FSEQ_DATA-request-has-the-same-rq_disk-as-the-original.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]kick queue after sequencing REQ_FLUSH/FUA https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-kick-queue-after-sequencing-REQ_FLUSH-FUA.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]initialize flush request with WRITE_FLUSH instead of REQ_FLUSH https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-initialize-flush-request-with-WRITE_FLUSH-instead-of-REQ_FLUSH.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]simplify queue_next_fseq https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-simplify-queue_next_fseq.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]filter flush bio's in __generic_make_request() https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-filter-flush-bio-s-in-__generic_make_request.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]preserve RHEL6.0 struct request_queue kABI https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-preserve-RHEL6-0-struct-request_queue-kABI.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]implement REQ_FLUSH/FUA based interface for FLUSH/FUA requests https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-implement-REQ_FLUSH-FUA-based-interface-for-FLUSH-FUA-requests.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199]
On 02/04/14 20:17, Alexandru Chiscan wrote:
On 04/02/2014 01:00 AM, Tom Robinson wrote:
On 01/04/14 17:49, Alexandru Chiscan wrote:
On 04/01/2014 06:27 AM, Keith Keller wrote:
On 2014-04-01, Tom Robinson tom.robinson@motec.com.au wrote:
Now, I understand that Red Hat (and therefore CentOS) backport many upstr= eam features into the stock kernel so how can I be sure that kernel 2.6.32-431.11.2.el6 has write bar= rier support?
Take a look here: https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/...
Regards, Lec
Thanks Lec, I did read this already. It does address filesystems but not LVM. Are write barriers enabled for LVM? Write barriers need to be implemented through the entire stack for them to work. If you have ext4 on LVM on MD not having them on LVM would break the chain. N'est-ce pas?
from the kernel changelog (https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11...) the barrier support for filesystems, lvm (dm) and md is active from 2.6.32-82-el6
-[fs]jbd2: replace barriers with explicit flush and FUA usage https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/fs-jbd2-replace-barriers-with-explicit-flush-and-FUA-usage.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[fs]jbd2: Modify ASYNC_COMMIT code to not rely on queue draining on barrier https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/fs-jbd2-Modify-ASYNC_COMMIT-code-to-not-rely-on-queue-draining-on-barrier.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[fs]jbd: replace barriers with explicit flush and FUA usage https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/fs-jbd-replace-barriers-with-explicit-flush-and-FUA-usage.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[fs]gfs2: replace barriers with explicit flush and FUA usage https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/fs-gfs2-replace-barriers-with-explicit-flush-and-FUA-usage.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[fs]btrfs: replace barriers with explicit flush and FUA usage https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/fs-btrfs-replace-barriers-with-explicit-flush-and-FUA-usage.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[fs]xfs: replace barriers with explicit flush and FUA usage https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/fs-xfs-replace-barriers-with-explicit-flush-and-FUA-usage.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]pass gfp_mask and flags to sb_issue_discard https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-pass-gfp_mask-and-flags-to-sb_issue_discard.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]disallow FS recursion from sb_issue_discard allocation https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-disallow-FS-recursion-from-sb_issue_discard-allocation.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[dm]convey that all flushes are processed as empty https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/dm-convey-that-all-flushes-are-processed-as-empty.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[dm]fix locking context in queue_io() https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/dm-fix-locking-context-in-queue_io.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[dm]relax ordering of bio-based flush implementation https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/dm-relax-ordering-of-bio-based-flush-implementation.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[dm]implement REQ_FLUSH/FUA support for request-based dm https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/dm-implement-REQ_FLUSH-FUA-support-for-request-based-dm.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[dm]implement REQ_FLUSH/FUA support for bio-based dm https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/dm-implement-REQ_FLUSH-FUA-support-for-bio-based-dm.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]make __blk_rq_prep_clone() copy most command flags https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-make-__blk_rq_prep_clone-copy-most-command-flags.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[md]implment REQ_FLUSH/FUA support https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/md-implment-REQ_FLUSH-FUA-support.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[virt]virtio_blk: drop REQ_HARDBARRIER support https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/virt-virtio_blk-drop-REQ_HARDBARRIER-support.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]loop: implement REQ_FLUSH/FUA support https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-loop-implement-REQ_FLUSH-FUA-support.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]use REQ_FLUSH in blkdev_issue_flush() https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-use-REQ_FLUSH-in-blkdev_issue_flush.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]update documentation for REQ_FLUSH / REQ_FUA https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-update-documentation-for-REQ_FLUSH-REQ_FUA.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]make sure FSEQ_DATA request has the same rq_disk as the original https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-make-sure-FSEQ_DATA-request-has-the-same-rq_disk-as-the-original.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]kick queue after sequencing REQ_FLUSH/FUA https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-kick-queue-after-sequencing-REQ_FLUSH-FUA.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]initialize flush request with WRITE_FLUSH instead of REQ_FLUSH https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-initialize-flush-request-with-WRITE_FLUSH-instead-of-REQ_FLUSH.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]simplify queue_next_fseq https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-simplify-queue_next_fseq.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]filter flush bio's in __generic_make_request() https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-filter-flush-bio-s-in-__generic_make_request.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]preserve RHEL6.0 struct request_queue kABI https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-preserve-RHEL6-0-struct-request_queue-kABI.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199] -[block]implement REQ_FLUSH/FUA based interface for FLUSH/FUA requests https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11.2.el6/patches/block-implement-REQ_FLUSH-FUA-based-interface-for-FLUSH-FUA-requests.patch (Mike Snitzer) [635199 https://bugzilla.redhat.com/show_bug.cgi?id=635199]
Thanks Alexandru,
I did look at the changelog but, for my untrained eye, I saw no specific reference to LVM there (and indeed still don't in your list above). Are you saying that because dm is patched, LVM is now implementing barriers correctly?
Kind regards, Tom
On 04/03/2014 06:25 AM, Tom Robinson wrote:
On 02/04/14 20:17, Alexandru Chiscan wrote:
On 04/02/2014 01:00 AM, Tom Robinson wrote:
On 01/04/14 17:49, Alexandru Chiscan wrote:
On 04/01/2014 06:27 AM, Keith Keller wrote:
On 2014-04-01, Tom Robinson tom.robinson@motec.com.au wrote:
Now, I understand that Red Hat (and therefore CentOS) backport many upstr= eam features into the stock kernel so how can I be sure that kernel 2.6.32-431.11.2.el6 has write bar= rier support?
from the kernel changelog (https://access.redhat.com/knowledge/sources/source_rpms/kernel-2.6.32-431.11...) the barrier support for filesystems, lvm (dm) and md is active from 2.6.32-82-el6
Thanks Alexandru,
I did look at the changelog but, for my untrained eye, I saw no specific reference to LVM there (and indeed still don't in your list above). Are you saying that because dm is patched, LVM is now implementing barriers correctly?
As what I know the LVM system is implemented on top of dm (device mapper) (see http://en.wikipedia.org/wiki/Logical_Volume_Manager_%28Linux%29) so it should handle the barrier requests if dm does it.
<quote> In the 2.6-series of the Linux Kernel, the *LVM is implemented in terms of the **device mapper http://en.wikipedia.org/wiki/Device_mapper*, a simple block-level scheme for creating virtual block devices and mapping their contents onto other block devices. This minimizes the amount of relatively hard-to-debug kernel code needed to implement the LVM. It also allows its I/O redirection services to be shared with other volume managers (such as EVMS http://en.wikipedia.org/wiki/Enterprise_Volume_Management_System). *Any LVM-specific code is pushed out into its user-space tools, which merely manipulate these mappings and reconstruct their state from on-disk metadata upon each invocation.* </quote>
Regards, Lec
Kind regards, Tom
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