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Re: [Linux-cluster] GFS Multi-pathing and trespassed LUNs

On Jun 6, 2005, at 1:13 AM, <JACOB_LIBERMAN Dell com> wrote:

This is a question regarding GFS native multipathing support:

I have a typical redundant mesh topology -- 2 switches, 2 HBAs per host,
2 storage processors. I create the pool device per the procedure
outlined in RedHat KB 4343 and then mount it locally. This works fine.
However, if I trespass the LUN between SPs during a write operation, I
lose all access to it. I have tried pool_mp with both failover and round
robin policies.

Unfortunately, pool multipathing does not do any special handling when switching between LUNs - it assumes all LUNs are active/active. This does not seem to be the case in your instance, as trespassing LUNs is a way to do active/passive multipathing (IIRC). So, to answer your questions....

Here are my questions:
1. Is there any way to accommodate trespassed LUNs via pool_mp?

Short answer: no.

Long answer: yes. However, you would have to purchase a copy of PowerPath and use that for multipathing. Pool understands powerpath devices and will sit happily upon them - ignoring the other paths to the device.

With multipathing in RHEL4, underlying hardware idiosyncrasies are dealt with properly.

2. Do you need to do anything special (ie remount the LUN, run
partprobe, etc.) to accommodate a trespassed LUN?

If it were possible to make the non-useable LUNs unseen to linux, at least you would have fault tolerance down to the device... However, this would mean that if a controller failed, you wouldn't be able to handle it.

3. are the pool_mp policies primarily designed to accommodate front-end
failures? (IE cables, HBAs, switch ports.)

Again, pool MP requires that all paths are active/active.

hope this helps,

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