Wasisnt
Contributor
Contributor

What makes a storage path standby compared to active?

Jump to solution

I was looking around in our new vSphere 4.1 installation and noticed in the manage paths section of a datastore that there are the 2 iSCSI connections listed but one says active and one says standby. Wouldn't it be better to have them both active so they could be used at the same time? We will be adding more connections and it would be nice to utilize them at the same time. How do you go about changing that or is that done by the path selection type? (see attachment)

0 Kudos
1 Solution

Accepted Solutions
mcowger
Immortal
Immortal

Here's how it works:

When a storage array is attached, vSphere interrogates the array to determine its capabilities.  From that, it determines which path selection plugin to use.

Given your screen shots, it looks like you have some form of LSI array, most of which are ALUA arrays.  For a description of what that really means, read my blog post, then come back: http://blog.cowger.us/2011/07/03/alua-active-arrays/

By using the information the array provides, the host (vSphere) can determine which paths are 'optimal' (and should therefore be active) and which are not (they would incur a usage penalty and should be standby only).

Under 'Fixed' pathing, the host uses only the path defined to send commands/data unless its unavailable, in which case it will switch to a secondary path.  When the primary path comes back, it switches back.  Fixed pathing is somewhat uncommon these days.  You use only 1 path, and 1 controller at a time.

Under MRU pathing, the host uses the Most Recently Used path to send commands/data, and switches only when the path in use is unavailable.  It does not switch back automatically (to prevent some LUN trespassing issues).  You use only 1 path, and 1 controller at a time.

Under round robin, the host switches rapidly (by default every 1000 commands) between all *active* paths (those reported by the array to be optimized).  You still only  use  1 path, and 1 controller at a time, but you switch between them.

Using the default vSphere multipathing plugin, there is no way to simulataneously use more than 1 path at any given time.  To do that you'd need some form of true load balancer, which are generally addons.  The only ones I know of that do this are the Equallogic MEM (only useable with EQL arrays) and the EMC PowerPath/VE plugin, which can use all paths to storage simultaneously (with EMC and certain other arrays).

Hope this helps.

(disclaimer, I work for EMC).

--Matt VCDX #52 blog.cowger.us

View solution in original post

0 Kudos
4 Replies
PduPreez
VMware Employee
VMware Employee

Hi

The default Path selection are MRU (Most recently Used)

Depending on the best practise guide of the Storage being used, you could change it to round robin.

See tread : http://communities.vmware.com/message/1821650

regards

Pieter

Please award points if this is helpful or correct Smiley Happy

0 Kudos
Wasisnt
Contributor
Contributor

Does the path selection type determine if both/all the paths are used? Is there a way to keep the path selection type but enable the other connection?

0 Kudos
mcowger
Immortal
Immortal

Here's how it works:

When a storage array is attached, vSphere interrogates the array to determine its capabilities.  From that, it determines which path selection plugin to use.

Given your screen shots, it looks like you have some form of LSI array, most of which are ALUA arrays.  For a description of what that really means, read my blog post, then come back: http://blog.cowger.us/2011/07/03/alua-active-arrays/

By using the information the array provides, the host (vSphere) can determine which paths are 'optimal' (and should therefore be active) and which are not (they would incur a usage penalty and should be standby only).

Under 'Fixed' pathing, the host uses only the path defined to send commands/data unless its unavailable, in which case it will switch to a secondary path.  When the primary path comes back, it switches back.  Fixed pathing is somewhat uncommon these days.  You use only 1 path, and 1 controller at a time.

Under MRU pathing, the host uses the Most Recently Used path to send commands/data, and switches only when the path in use is unavailable.  It does not switch back automatically (to prevent some LUN trespassing issues).  You use only 1 path, and 1 controller at a time.

Under round robin, the host switches rapidly (by default every 1000 commands) between all *active* paths (those reported by the array to be optimized).  You still only  use  1 path, and 1 controller at a time, but you switch between them.

Using the default vSphere multipathing plugin, there is no way to simulataneously use more than 1 path at any given time.  To do that you'd need some form of true load balancer, which are generally addons.  The only ones I know of that do this are the Equallogic MEM (only useable with EQL arrays) and the EMC PowerPath/VE plugin, which can use all paths to storage simultaneously (with EMC and certain other arrays).

Hope this helps.

(disclaimer, I work for EMC).

--Matt VCDX #52 blog.cowger.us

View solution in original post

0 Kudos
Wasisnt
Contributor
Contributor

Now that clears it up quite a bit. Thanks for the info!

We use IBM DS3512s by the way.

0 Kudos