Dell EqualLogic PS4000E review

Dave Mitchell Read more October 7, 2009

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£21275

Price when reviewed

Dell’s latest member of the EqualLogic family of IP SAN appliances, the PS4000E, aims to offer a more affordable alternative for medium-sized businesses. Not only does it deliver an impressive range of features but it could be one of the fastest appliances in its class.

The PS4000E supports a pair of controllers, and Dell offers a range of options to allow you to grow with demand, by opting for one or both controllers and either eight or 16 SATA drives. Each controller has two Gigabit data ports and a management port, and comes with 2GB of battery-backed-up cache and support for RAID6.

Physical appliances are gathered together in groups and presented as logical storage pools. Virtual volumes are created within these and presented as iSCSI targets, but the volume data is spread across all appliances and drives in the group. Note that the PS4000E is restricted to two appliances per group.

Installation is simple thanks to Dell’s Windows Remote Setup wizard. You choose a member name and assign it an IP address, pick your RAID array and join an existing group or create a new one. The two data ports are grouped together under a virtual IP address where the appliance carries out load balancing.

Dell’s Group Manager console provides easy access to functions such as group, storage pool and volume creation. For the latter you choose a storage pool, decide on a volume size and add access restrictions. Thin provisioning can be configured during volume creation and you decide how much physical space to start with. The appliance uses three watermarks, where the minimum size is 10% of the virtual volume. When the volume is 95% full the system starts throttling back I/O performance to allow administrators time to increase the volume size. Once you reach the critical watermark the volume is placed offline.

With snapshots you decide how much space to set aside, and at any time you can promote snapshots as new volumes. A thin provisioned volume will have its snapshots and replicas thinly provisioned, and you can swap between classic and thin provisioned volumes.

For replication, snapshots of selected volumes are stored in other groups called replication partners. During setup you can choose one-way replication to another group, bi-directional replication between groups, or designate one group as a central location to which multiple groups can be replicated. If a volume is lost or damaged, you can just clone a copy of the replicated volume.

Dell’s SAN HeadQuarters manages multiple appliances from a central console. You can view detailed reports on capacity, which show the total space for the group and how it’s split up into volumes and snapshots. A screen of combined graphs keeps you posted on network utilisation along with the number of logged-in hosts, and a separate screen provides a rundown on I/Os and average latency. The table for disk performance didn’t work, however, as most of the drives showed a zero throughput. The network option has a dial showing utilisation of the virtual network port and a group summary.

We tested it by creating a RAID10 member array with all available drives, and within this we configured two 50GB partitions with access limited to our test servers by their IP addresses. We used a Broadberry CyberServe system equipped with dual 2.8GHz X5560 Xeons plus 12GB of DDR3, a Boston rack server with dual 2.5GHz L5420 Xeons and 4GB of DDR2, with both running Server 2003 R2.

Starting with the CyberServe we logged on to the first virtual volume and ran Iometer, which reported a steady raw read throughput of 112MB/sec. We confirmed that the Boston system delivered the same speed when connected to its dedicated volume, and with both servers running Iometer simultaneously we saw a cumulative throughput of 218MB/sec.

We tested further using MPIO links. Setting these up was a cinch with Dell’s host integration tools: connect two physical network ports, log on to the portal and target, and Dell does the rest. Each server reported around 220MB/sec, and with both in the mix we saw this top out at a cumulative 227MB/sec.

The PS4000E is easy to deploy and is good value, including snapshots, thin provisioning and replication in the price. Add in top performance and expansion potential, and it’s one classy IP SAN appliance.