Review: Dell EqualLogic SANs make the most of automated tiering

Dell EqualLogic SSD and SAS hybrids highlight no-muss, no-fuss, fast storage tiering across multiple arrays

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Let's envision a fairly traditional storage workload for a medium-size infrastructure. We have a bunch of hypervisors driving several hundred VMs, along with general-purpose file sharing, and a passel of databases that drive a Web application tier to provide critical line-of-business applications.

It's common to satisfy all of these storage requirements through the same homogenous storage array, but there are drawbacks. For instance, it means that the long-forgotten, never-again-to-be-accessed 2GB movie file that a user once stored in his home directory will sit right next to the bits that the core database servers are constantly reading and writing. In a perfect world, these files wouldn't mix, but we all know that the world we inhabit is rife with similar examples.

With automated tiering, that neglected movie file will eventually wind up on the slowest disks in the data center, while the database volume will wind up on the fastest -- without any administrative intervention required.

In practice, this process is as simple as setting up the disparate arrays in the same group and introducing the workload. As the controllers get an idea of which data is flowing where, they will automatically distribute the blocks throughout the arrays according to the demand.

In our example, this would mean that the database volumes and high-transaction VMs would wind up on the SSDs, while the movie file winds up on the SATA drives. As the load changes, the solution automatically adapts. If the user shared a link to that movie with the entire company and the movie began streaming to a few hundred people, the controllers would migrate it to faster storage. Thankfully, the Dell EqualLogic SAN HQ software provides the controls to ensure that an odd workload change such as this does not bump more critical data sets from the fastest disk.

Another benefit of automated tiering is that weekly or monthly workloads can be granted the benefit of fast disk only when they actually need it. As a monthly batch job progresses and the responsible databases start churning for a 24-hour period, they will reap the benefits of the SSD-backed storage, then fall back to the slower disk as their processing completes. Another example might be a virtual desktop infrastructure that experiences heavy loads during the morning log-ins and the evening log-offs, when desktop VMs are being quickly spun up and put away, respectively, with lower disk I/O utilization in the middle.

Performance in numbers
Automated tiering isn't completely new to Dell EqualLogic, but the ability to extend the tiering across multiple high-speed and low-speed arrays such as the PS6110XS and the PS4110E puts the performance benefits in bold relief. Rather than having to add three or four arrays of differing storage types to fully realize the benefits, the PS6110XS accomplishes much the same goal internally, as it can drive both SSD and SAS drives in a single 24-disk 2U chassis. And demonstrating the effects of storage tiering is relatively simple, requiring only a repetitive workload that extends for a reasonable period of time.

Using IOMeter to test the PS6110XS and the PS4110E arrays was the simplest way to investigate the solution. When hit with a mix of streaming and random reads and writes, the throughput grew substantially in some cases, less so in others, depending on a wide variety of variables such as block size and the level of random reads and writes. As with any storage device, your mileage may vary depending on the workload, but my general-purpose testing shows that the combination of the PS6100XV and the PS4110E should adapt very nicely to most infrastructures.

By extending automated storage tiering throughout the EqualLogic product line, Dell has made it both simpler and less costly to implement an extremely useful storage management capability in the data center.

Dell EqualLogic iSCSI SANs with Automated Storage Tiering

Cost The EqualLogic line starts at a list price of $16,000 for the PS4100E; the PS6110XS has a list price of approximately $96,000
Operating systems supported Windows Server 2000/2003/2008/2008 R2, VMware ESX Server, Citrix XenServer, Red Hat Enterprise Linux, Novell Suse Linux Enterprise Server, Oracle Solaris, IBM AIX, HP-UX, Mac OS X, Novell NetWare

This story, "Review: Dell EqualLogic SANs make the most of automated tiering," was originally published at Follow the latest developments in storage, data management, and data protection at

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