Linux multipath.conf (Multipathd)

We had an EqualLogic controller fail-over at the weekend for some reason (fw 8.13) which resulted in some of our virtual machines getting paused (I have raised a case on techdirect about the array itself).

We use ovirt / kvm and someone at redhat has helpfully suggested that we make the following adjustments to multipathd config ( I am aware there is no support agreement for this):

You can set the timeout in multipath.conf.

If you want to allow 60 seconds gracetime in such case, you can configure:

no_path_retry 12

This will continue to monitor the paths 12 times, each 5 seconds

(assuming polling_interval=5). If some path recover during this time, the io

can complete and the vm will not be paused.

Can anyone see any major issues with these suggestions ?

The majority of our guest disks are set to timeout after 60 seconds internally within the vms themselves.

Thanks

Responses(2)

SAE_StevenL

1 Message

1

October 5th, 2016 08:00

Hi G110YD - Thanks for posting this question to the forum.

I recommend not using a numeric value for the "no_path_retry" variable within /etc/multipath.conf as once that numeric value is reached, if no healthy LUNs were discovered during that defined time multipath will disable the I/O queue altogether.

I do recommend, however, changing the variable value from "12" (or even "60") to "queue" which will then allow multipathd to continue queing I/O until a healthy LUN is discovered (time of fail-over between controllers) and I/O is allowed to flow once again.

A recent publication concerning the Best Practices around Dell PS Series storage and SLES 12 SP1 host configuration covers some of the /etc/multipath.conf values in more detail. This guide can be found here

It may be of some benefit to you, if not locked into native iSCSI on RHEL, to look into the Dell EqualLogic HIT/Kit (Host Installation kit) for Linux to handle the MPIO of the host for you.

We, the Storage Applications Engineering team, produce many valuable documentation resources around Linux configuration of both Dell PS (EqualLogic) and Dell SC (Compellent) Storage, which can be found at: www.dell.com/StorageResources

A

Anonymous

5 Practitioner

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274.2K Posts

1

October 6th, 2016 14:00

Additionally,

With the firmware docs is a PDF that has info on extending the DISKTIMEOUT for Windows and Linux, This will also better allow Linux to handle the controller failover,

Regards,

Don

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