Six iSCSI SANs unleashed
Adaptec, Celeros, EqualLogic, Intransa, NetApp, and Rasilient move our megabytesFollow @pvenezia
After the controllers had been configured on the network, all further administration was handled by the Java-based Web GUI. I found the UI to be well-organized and quite versatile, although I did run into problems related to the JRE (Java Runtime Environment) version on a few workstations. I settled on a revision of 1.4.2 that seemed to play nice and created my volumes. As with most iSCSI targets, each volume can be assigned access rights to permit only certain initiators to connect and mount any given volume. The iSCSI standard calls for the use of CHAP, which provides a modicum of initiator authentication, and the PS200E handles that without an issue. Also, initiators can be assigned to LUNs by mapping the initiator IQN to that LUN. Volume presentation is then determined by the requesting initiator IQN. There is no means of grouping or aliasing IQNs, which can get tedious when working with several servers.
I configured the PS200E for performance, running the array at RAID 10 with two hot spares. RAID 10 is a mirror set of striped arrays, providing better performance than RAID 5 while maintaining redundancy via the mirror. The downside is that only 50 percent of the raw capacity of the filer is usable. But with SATA drives reaching 500GB per spindle, this isn't the constraint it once was.
In performance tests, the PS200E led the field, claiming the highest marks in the raw single-threaded read tests and showing a superlative 101MBps 256KB streaming write throughput with the Alacritech iSCSI accelerator on Windows. Interestingly, the PS200E also responded well to the QLogic HBA, posting the best file creation and deletion times -- especially impressive considering the HBA's lack of jumbo frame support. Overall, the EqualLogic PS200E posted the best raw iSCSI performance numbers in the test.
When I built the second PS200E, I initially created a completely separate group for it and configured replication between the arrays. This is extremely simple to do, and the PS200Es will do a block-level synchronization of volumes at scheduled intervals or when manually triggered. The controllers provide no bandwidth shaping, however, so factor that into your plans if you're replicating over WAN links.
After resetting the second PS200E to factory defaults, I joined it to the original array group -- again, very simple -- and was able to manage both arrays from the group UI. When joined, the two units immediately reallocated volumes between them for better load balancing -- a very nice touch. The downside of this is that a failure of one of the group members can affect all the volumes between both units, bringing everything to a halt.
When you add arrays to an EqualLogic storage group, you not only add disk, you add controllers. Each set of controllers in the array has three active Gigabit Ethernet interfaces and uses active load balancing between them to balance server requests. The interfaces on the dormant controller can be used as fail-over interfaces as well. Thus, as you add more disk, you also add more network capacity -- another nice feature.