When to use the fixed path policy? when to use the most recently used path policy
From the ESX 3.5 Configuration Guide page 135 and 136
The Most Recently Used policy is required for active/passive storage arrays, in
which one storage processor remains passive waiting for the other to fail.
VMware recommends the Fixed policy for active/active storage arrays, in which all
storage processors can pass the storage traffic and all paths can be active at all
times, unless a path fails. Most iSCSI storage systems are active/active.
/Rubeck
The supported storage guide specifies the optimal policy for each supported array.
In general, an active/active array shoudl use MRU or fixed path, an active/passive array will use MRU.
--Matt
By default, ESX 3.5 uses:
- Most Recently Used (MRU) policy for FC storage and
- Fixed path policy for iSCSI storage.
Most iSCSI storage arrays are active/active where more than one path are active at any time and most FC storage arrays are active/passive where only one path is active at any time.
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To add here, the recommendation as mcowger defined is mru for active/active and fixed for active/passive.
An active/active array will allow either controller to present the disks on that array, so in the event of a failure of one controller, the active path will shift to the active controller. On the ESX side, the policy of MRU will not use this new path for all future communication to the disk, even if the failed controller comes back up. This prevents disk thrashing. In an active/passive, when the failed controller comes back up, it will attempt to take over the disks that failed, and the activity will shift, and this can go on and on causing severe performance degradation.
So, active/active, pick MRU and stick with whatever controller you see, and active/passive, use fixed.
Also, if you want to load balance or round robin your connections over your available paths, then you will most likely be using fixed anyway, even if you have active/active.
-KjB
From the ESX 3.5 Configuration Guide page 135 and 136
The Most Recently Used policy is required for active/passive storage arrays, in
which one storage processor remains passive waiting for the other to fail.
VMware recommends the Fixed policy for active/active storage arrays, in which all
storage processors can pass the storage traffic and all paths can be active at all
times, unless a path fails. Most iSCSI storage systems are active/active.
/Rubeck
