[linux-lvm] Re: LVM + Multipathing

[Ritesh Raj Sarraf <rrs@researchut.com>]

Luca Berra wrote:

> On Sat, Feb 17, 2007 at 09:52:27PM +0530, Ritesh Raj Sarraf wrote:
>>Hi,
>>
>>I have a question regarding the combination of LVM + Multipathing in a SAN
>>environment.
>>
>>I have a LUN mapped to a host using iSCSI. I have two two paths to the LUN.
>>This setup, using multipathing, provides me failover functionality.
>>
>>My question is how does LVM react to path failures ?
>>In a failover environment, multipathing can take upto 120 seconds to detect
>>that the active path to the LUN is no more available and then switch to the
>>secondary path. During this 120 seconds, how does LVM react ? Does it really
>>sense that the device is offlined ? Or that information is never passed to LVM
>>and it just allows I/O to happen leaving that responsibility to the
>>multipathing layer ?
> 
> i believe LVM does not react at all.
> 

I brought this question because I'm seeing Filesystem READONLY issues when doing
a takeover/giveback.

My understanding is that a filesystem usually goes read-only, only when it
senses errors in the drive. Now I believe LVM might the culprit because beneath
the filesystem and above the block device, LVM is the only layer.

Thanks,
Ritesh
-- 
Ritesh Raj Sarraf
RESEARCHUT - http://www.researchut.com
"Necessity is the mother of invention."
"Stealing logic from one person is plagiarism, stealing from many is research."
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