High Availability / Clustering

[Lee <lee_hoffman@brown.edu>]

Ive read through most of the archives concerning high-availability 
options for openldap. Right now, we're trying to create make our ldap 
infrastructure highly-available, as well as load-balanced between three 
servers (more to be added later). From my research it seems like we 
have a few options:

1) Experimental Multi-Master: This seems to have a number of atomicity 
issues. Plus this doesn't really solve the problem with the ldap 
clients not appropriately using the second listed server if the first 
goes down.

2) Plain old Master + Multiple Slaves: Same second issue above, plus no 
high availability on writes.

3) Master + Slaves, Promotion of Slave if master goes down: Same ldap 
client not using second listed server problem as in 1) and 2) above, 
plus lots of issues with reclaiming Master status after failure.

4) 1 Master Server Cluster using shared storage: This seems like the 
only viable solutions. The problem is we need support for many servers 
connecting to one shared storage device, as well some sort of reliable 
locking mechanism thats compatible with openldap.

Has anyone successfully implemented 4) ? If so can you recommend any 
specific hardware and or software that works nicely with openldap?


Thanks,
L