Theres no denying that 4Gbps fibre channel (FC) technology has suffered from an indifferent marketing campaign during 2005 and its clear that this is an opening for iSCSI vendors to push home the advantage. EqualLogic specialises in IP SAN solutions and its latest PS300e iSCSI storage appliance shows clearly the advantages to be had with this technology.
This 3U chassis offers fourteen hot-swap bays and the system is supplied with a full compliment of 500GB Hitachi Deskstar 3Gbps SATA hard disks for an impressive total of 7TB. The appliance offers masses of redundancy with a pair of controllers mounted on solid sleds and easily removed from the rear. They deliver a fine specification which centre round 64-bit dual core RISC processors. RAID functions are protected by 1GB of PC2700 cache memory looked after by an integral battery backup pack whilst the firmware is implemented on a simple CompactFlash card. All RAID parameters are synched across both controllers so you can lose one without any impact on operations. Network connections abound as each controller is equipped with three copper Gigabit Ethernet ports or you can use the dual personality fibre mini-GBIC port instead for longer connections. The ports on the secondary controller provide redundancy and the primary controller automatically implements adapter teaming as each port is activated so the more you use the greater you can increase the network bandwidth which, in theory, could go up to 3Gb/sec.
EqualLogic uses a simple concept for gathering multiple arrays together which does offer a number of very useful features. Each physical array is referred to as a member and multiple arrays are placed in a single storage pool, or group. The array implements its own RAID protection but all storage within a group comprising multiple members is made available to the network as a single entity. Essentially, all storage space within the group can be carved up into volumes and presented as iSCSI targets but data within each volume is spread across all disks and members. There are big advantages here as new arrays can be added to the group on the fly allowing storage to be increased easily with demand. Network traffic is automatically load balanced across multiple network ports and you can use the secondary controllers to create redundant network connections as well.
Installation is handled nicely as you start with a serial port connection to the primary controller. We started with a single array and from the CLI to define it as a member and create our storage pool group. All RAID configuration is handled automatically but the controllers only support either RAID-10 or RAID-50 arrays - it would be good to see the latest RAID-6 and -60 supported. To select an array type you simply choose the Performance or Capacity options from the CLI. The array will configure the selected RAID type and automatically designate drives as hot-standby units. EqualLogic claims you can be up and running inside of twenty minutes from unpacking the box and from our experiences we have to agree.
For performance testing we connected a single array to a Gigabit Ethernet network and used three dual Xeon servers running Windows Server 2003 and equipped with the Microsoft iSCSI initiator v2.0. To test raw throughput we called in the open-source Iometer and configured it to use two disk workers, 64KB sequential read transfer requests and ten outstanding I/Os. We opted for the performance settings and allowed the appliance to create an eight disk RAID-10 array after which we created a single 50GB volume. Starting with one Gigabit Ethernet connection to the appliance and a single server logged on to the iSCSI target volume we saw Iometer report a stunning 112MB/sec throughput for read operations. We then activated the second Gigabit port on the appliance, added a second server logged on to the same volume and saw Iometer report a cumulative throughput of 214MB/sec. It gets even better as we then connected the third Gigabit port and added another test server also logged on to the same volume as the other two. This time Iometer reported a cumulative raw read throughput of no less than 300.5MB/sec thus confirming EqualLogics claims.
General management and monitoring is carried out from EqualLogicss smart Java-based web interface. From a simple menu to the left you can see each group member and selecting one shows plenty of operational information where you can drill down and view graphs on specific components. With a second PS300e appliance to hand we found it easy enough to add it as a new member as you define the group details and password from its CLI after which it is automatically added. If you decide to remove a member appliance you wont lose any data as the system automatically moves any resident data across to the other members before taking it out of the group.
Volume replication provides an extra layer of fault tolerance and good disaster recovery capabilities as you can use it to take snapshots of volumes on one group and place them on another group possibly in a different geographical location. We tested this by removing one member from our original test group and using it to create another group on the same network. You then declare it as a replication partner and associate it with a primary group. In the event of a disaster you can simply clone the copy or promote it as a new volume. EqualLogics replication features are very versatile as you can replicate a volume to another group, replicate volumes bi-directionally and designate multiple volumes within different groups to be replicated to a central storage group.
The PS300e shows clearly the potential of iSCSI at the enterprise level and makes IP SANs much more appealing as an alternative to FC SANs. Another advantage of EqualLogics product family is the choice on offer as the entry-level PS50e starts at £15,500 and comes with seven 250GB SATA drives and a single controller but uses exactly the same chassis allowing it to be upgraded as required.
The number and quality of features offered by the PS300e puts it on a par with many FC storage solutions. It?s got performance, fault tolerance, massive storage capacity and plenty of options to expand easily but above all else it delivers them at a price point that compares extremely well with equivalent FC products