Review: Dell EqualLogic iSCSI SAN kicks it to 10G

EqualLogic iSCSI storage arrays have always been fast, but they've recently gotten even faster. The new EqualLogic PS6010XV traded the four Gigabit Ethernet ports per controller in the PS6000 series in favor of two 10G Ethernet ports on each of the redundant controllers in the array. The result? Lower latency and snappier storage.

On one hand, bringing 10G to iSCSI arrays is a no-brainer. The per-port costs are still quite considerable, but in highly transactional roles, there's a tangible difference in storage access times. Suffice it to say, if you're bumping up against a 4Gb ceiling, 10G is very attractive.

[ Think you can't afford a SAN? See "Buy an 'expensive' SAN and save money" and "Is cheap disk storage really cheap?" ]

As with all EqualLogic iSCSI arrays, the PS6010XV is a self-contained, 4U, 16-drive unit available with 15K RPM SAS disks. The rear sports two redundant controllers and two redundant power supplies. The 10G connections are SFP+ -- no muss, no fuss. Firing up the array takes only a few minutes with a serial console, and subsequent configuration is handled through the well-appointed Java-based management app. All in all, it's almost faster and easier to set up a PS6010XV than it is to write about the process.

Easy setup and smooth scaling Proving once again that simple tends to be better, the PS6010XV integrates seamlessly into an existing EqualLogic storage group. If you have a collection of EqualLogic arrays, the PS6010XV will plug right into the management infrastructure. Thus, there is no learning curve to climb for implementation. Aside from the performance boost and the 10G interfaces on the controllers, the PS6010XV is one of the gang, so to speak.

It's quite hard to stress a 10G link to a single array of 16 drives unless they're solid-state drives (SSDs), which are not supported in the PS6010XV model. There are several models in the PS6010/PS6510 line, however, including the PS6010S, which does use SSDs, and the PS6510X, which offers up to 48 10K SAS drives. These models will make better use of a 10G link than a 16-spindle array will, due to the speed of SSDs and the increased spindle count in the PS6510X. Nonetheless, the 10G links aren't wasted on the PS6010XV.

EqualLogic's model of array scaling necessitates adding network capacity simultaneously with storage capacity. You can't attach raw disks to an EqualLogic array; it's all one unit, Ethernet ports included. That means adding 10G connectivity isn't so much about the bandwidth it can push, but rather about the lower latency and access times, which can have a significant impact on a variety of highly transactional applications. That's not to say the PS6010XV can't push beyond single gigabit limits, as I was able to get over 200MBps streaming reads from a single host, but that's nowhere near 10G boundaries.

The controllers in the PS6010XV are truly redundant. Although there are four 10G ports between them, only two are active at any one time. Should an interface or controller fail, the redundant controller will immediately and seamlessly take over. In fact, it's even possible to upgrade the controller's firmware on the fly with no downtime. The passive controller is upgraded, then takes charge as the primary controller is updated, allowing the process to complete without losing a packet.

It's this type of enterprise feature that can make a huge difference in data center operations, especially storage functions. It's never a good time when dozens and dozens of servers need to be powered down in order to upgrade the back-end storage.

Beyond gigabit throughput The lab setup for the PS6010XV was fairly simple: a Dell PowerEdge R710 server with 96GB of RAM and two Intel Xeon X5590 CPUs, a dual-port Intel 10G interface card, and a Dell PowerConnect 8024 24-port 10G switch in the middle. The R710 ran Windows Server 2008 R2 Datacenter, as well as VMware ESX 4 and CentOS 5.4 for a variety of tests. The PS6010XV was equipped with 16 600GB 15K SAS drives in a RAID 10 array (price as tested, $68,200).

Overall, the performance surpassed that of EqualLogic's gigabit-based arrays, easily eclipsing gigabit throughput during streamed reads and pushing over 200MBps when pulling directly from the controller cache in a 32K streaming read test, while a closer raw read beyond the cache pulled in around 160MBps. Write performance was necessarily lower, but still came in at 130MBps on a 32K streaming write test. The random access times were an impressive 2.8ms, with a streaming access time of 1.84ms. Some other highlights were the 26,000 IOps reached during a 2K streaming read at 50MBps and a 182MBps transfer rate on a 256K 50/50 random read/write test. There's no doubt this is a fast array, helped considerably by the oodles of cache.

Like any array, the PS6010XV is quite dependent on a battery-backed write cache. Disabling that cache leads to significantly reduced write speeds, so it's important to ensure that your workload doesn't push that cache beyond its limits. There's a total of 4GB of cache in the array, and that's a large part of the overall performance.

The array can support RAID 5, 6, 10, and 50, and the RAID levels can be configured on a per-array basis. The functional RAID level can be modified later on the fly, but only in certain circumstances. For instance, you can convert from a RAID 50 to a RAID 5 or 6, but not to a RAID 10.

The PS6010XV can also support up to 512 snapshots per volume, or up to 10,000 total snapshots, which should be more than enough for any implementation. Snapshots are configured on a per-volume basis and can be scheduled directly from the management interface.

SAN Headquarters The one thing missing from the Dell EqualLogic Group Manager is performance information. There's no facility to monitor array or group performance. However, Dell has a companion tool called Dell EqualLogic SAN Headquarters that closes that gap.

The tool installs on a server and communicates with the storage arrays via SNMP, gathering information on just about every aspect of the array, from network and disk I/O to overall array health. You can view IOps on a global or per-disk level, in addition to deep statistics like average disk queue depth.

The application is laid out well, and it's very simple to drill down to the data you're looking for, and just as simple to export it as a CSV file to be imported into any number of other applications. There's also a report creation engine that allows you to select any number of monitored items to be included in an attractive PDF generated by the utility. One of the handy predefined reports is a top 10 list that shows information such as the leading volumes by capacity, IOps, snapshots, and so forth. The predefined reports include configuration, capacity, replication, performance, host connection, and a hardware and firmware informational report. And you can choose from several different report templates.

The information gathered by SAN HQ is available for as long as the tool has been running and can easily show trends in usage. Overall, SAN HQ provides a great view into the workings of an EqualLogic storage infrastructure of any size.

EqualLogic has always seemed to be ahead of the curve in iSCSI storage, and the company's arrays provide a significant level of reliability, manageability, and performance. They're definitely not the cheapest iSCSI solutions out there, but they're a very good fit for those infrastructures that want to leverage the lower cost of iSCSI against significant performance needs.

If your storage needs surpass what Gigabit Ethernet can deliver, but you don't want to bite the expensive Fibre Channel bullet, check out the PS6010XV. With two 10G Ethernet interfaces, fully redundant controllers, blazing performance, and low latency, it offers performance on par with that of some Fibre Channel arrays but with a lower cost and simpler implementation.

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