Hi

We have some documentation for setting up stash here:
https://confluence.ez.no/display/EZP/Persistence+cache

However, currently the situation is as follows:
#1if singlemode and apc is availabe, use apc
#2if singemode and apc is not available, use BlackHole
#3if clustermode use BlackHole
This is what is going to be certified for 5.1

FYI : once a bug in stash is fixed, #2 can be changed into ( probably for ezp 5.2):
#2b if singemode and apc is not available, use Filesystem
However, 5.1 will not be certified and supported with this setting

Also, in clustermode, it is technically possible to use memcached, but that is not certified and supported.
This should be made a bit clearer in the doc
Also, correct stash settings must be mentioned in the cluster setup documentation, or people will easily run cluster mode with incorrect stash settings