[CentOS] write barrier support in CentOS 6

Alexandru Chiscan lec at chiscan.dnsalias.org
Thu Apr 3 06:49:54 UTC 2014


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 at 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-2.6.32-431.11.2.el6/changelog)
>> 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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-- 
Lec




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