[rhelv6-list] RHEL6 write barriers on MD and LVM devices

[Tom Robinson]

On Sat, Mar 15, 2014 at 9:54 AM, Jason Keltz <jas cse yorku ca <mailto:jas%20cse%20yorku%20ca>> wrote:

    Hi everyone..
    I've seen a lot of conflicting information with respect to support of write barriers on MD and
    LVM devices under RHEL6.  I'm surprised that this question hasn't come up on this list before!
    I'm building a system with MD RAID10, and putting LVM on top of it, using ext4 filesystems.  I'd
    like to know whether write barriers are supported through the complete chain in this
    environment.   When I mount the filesystems, there are no kernel errors that barriers are not
    supported, but I don't want to be under the false impression that barriers "appear" to be
    supported, yet are not.  For example, I've read that barriers were only supported on MD at all
    levels in 2.6.33 (previously only RAID1). While RHEL6 is based on 2.6.32, I "assume" that RH
    would backport an important change like that, or, at least have a warning in the documentation,
    but I can't find any mention of this.  I've also read quite mixed messages about barrier support
    in LVM as well. Any help would be much appreciated.


Hi,

I've searched for a solid answer to this question myself but so far I'm still in the dark. Can
anyone categorically state for the record (or point to some clear documentation) whether or not
write barrier support is indeed implemented for LVM under RHEL 6?

My expectation is that LVM write barrier support will have been back-ported to the current 2.6.32
RHEL kernel. I've googled until my fingers and eyes are sore but I can't find anything to support
that assumption. I looked here, too:

 https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html-single/6.5_Technical_Notes/index.html

But it's inconclusive as to the support for write barriers in LVM.

Help please. Anyone?

Kind regards,
Tom


-- 

Tom Robinson
IT Manager/System Administrator

MoTeC Pty Ltd

121 Merrindale Drive
Croydon South
3136 Victoria
Australia

T: +61 3 9761 5050
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