The SMB sector is poised to become the next big market for SANs. For vendors courting this market, the biggest challenge is that because SMBs typically lack specialized storage architects and administrators, building SANs from components is a tricky proposition for them.
To see how some of the major players are addressing this issue, I looked at SMB-friendly SAN offerings from Compellent, Dell/EMC, Dynamic Network Factory, Hewlett-Packard, IBM, iQstor, MPC, and Nexsan. Of the eight systems tested, three offer FC (Fibre Channel), three offer iSCSI (Internet SCSI), and two offer both forms of connectivity.
Although marketed to smaller shops, these are enterprise systems at their hearts -- with some capable of scaling to dozens or even hundreds of terabytes. Easy to set up and use, each system offers performance suitable for all but the most demanding, specialized applications. You might assume iSCSI wouldn’t offer performance on par with that provided by FC, and this would be true for iSCSI over Gigabit Ethernet as compared with a 2Gbps FC link. But iSCSI can run over 10 Gigabit Ethernet, and with the right hardware and software in place, that combination could easily outperform 4Gbps FC.
Similarly, although the systems tested use FC, SCSI, or SATA drives, a drive’s performance isn’t necessarily a good indicator of the overall performance of a SAN system. The storage processor, network interface, caching, HBA, and other components can affect performance just as much or more than drives do. In my tests of the eight systems, I found no startling differences in performance. Regardless of the type of interface or drive used, all proved more than capable of filling the bandwidth to the box.
Some people make an issue of the greater MTBF (mean time between failures) of FC and SCSI drives (1 million hours or more) when compared with those of SATA and ATA drives (400,000 hours or more). But even with a 400,000-hour MTBF, assuming an active life of five years (approximately 43,800 hours), it’s likely that a SATA drive would be replaced before it would fail, and it is capable of providing three times the capacity of an FC or SCSI drive at a quarter of the cost.
A complete FC SAN system includes HBAs, a switch or direct cable connection from server to storage, and the storage subsystem. Dell/EMC and HP provide complete kits with FC HBAs, switches, and storage arrays. These kits make the installation and configuration of a SAN simple -- no worrying about getting matching components or whether they will work together properly. Both the Dell/EMC and HP systems include easy installation and RAID management software that make it easy to get the systems running.
This is not to say the other systems are difficult to install. The days of having to input long identification strings before HBAs and storage arrays can communicate are past. All the FC systems were easily autodiscovered and configured, and the software included with each system provided easy configuration and management.
Technically speaking, iSCSI systems don’t need HBAs -- the iSCSI drivers included with Windows Server 2003 and available for Linux will allow you to use any Ethernet adapter to connect to an iSCSI storage array. For optimum performance, however, you should consider an Ethernet adapter that offloads iSCSI processing, which reduces the load on the server and optimizes network communications. Likewise, you’ll get better performance running iSCSI over an Ethernet network that is separate from the company LAN.
The choice between iSCSI and FC comes down to price vs. performance. For a given capacity, there isn’t a huge price difference between iSCSI and FC storage arrays, but iSCSI (Ethernet) switches and iSCSI HBAs are much less expensive than FC switches and FC HBAs. On the other hand, 2Gbps FC is more than twice as fast as iSCSI over Gigabit Ethernet. Given the relative volumes of Ethernet vs. FC sales and the rate at which 10 Gigabit Ethernet prices are dropping, it may not be long before 10Gbps iSCSI is cheaper than 2Gbps FC -- and it will be cheaper than 4Gbps FC even sooner.
Since all the products in this review offer relatively simple installation and administration, the prime differentiator -- after you choose FC or iSCSI -- will be the storage management features available. These features include snapshots, backup, replication, remote replication, on-the-fly expansion of existing partitions and volumes, the ability to change RAID levels without disrupting stored data, and more. Whether you’ll want these features will depend on what you’re using the storage for and whether you already have storage management software.
One final issue you’ll want to consider is that disk drives for a given array are typically available only from the SAN system vendor. This is due to the need to qualify drives and ensure that they’ll operate with existing hardware. If you buy a system with less than a full load of drives, be aware that you’ll have to go back to the vendor for more drives as necessary. The exception to this is the HP system, which uses the same Ultra320 SCSI drives that are available from many retailers for use in HP servers.
Compellent Storage Center QuickStart
Compellent’s QuickStart is considerably more expensive than the other systems in this test, but it also delivers exceptional performance, ease-of-use, and features that the other systems don’t have. Compellent even includes on-site support for the initial QuickStart installation.
The Compellent system consists of two parts: the storage controller (housed in a separate 2U box) and one or more storage units. The storage units hold as many as 16 disk drives -- either FC drives or SATA drives or both, allowing you to include a high-performance database volume and a cheap file-server volume in the same unit, for example.
I received one storage controller and two storage units, one with nine Maxtor 250GB SATA drives and one with nine Seagate 147GB FC drives. The controller had four dual-port FC interfaces, and each storage unit had two dual-port FC interfaces (iSCSI is optional). All had redundant fans and power supplies.
The storage controller supports as many as three dual-connect, direct-attached storage units -- more if you use FC switches to connect additional storage units to the controller. After you have connected the storage unit to the controller and the controller to your server, the system is ready to run. After an initial network configuration via serial terminal, the rest of the configuration is done through a browser. The interface is straightforward and easy to navigate and includes useful online help. Users and groups can be configured with differing levels of access so that some administrators can be restricted to monitoring and viewing data, while others can be given the access necessary to make changes.
Administrators who are in a hurry or who aren’t sure exactly how they want to configure their storage will appreciate the Compellent system. Whereas some of the other storage arrays took a half hour or more to create a 300GB RAID 5 volume for the first time, the Compellent system created a 2TB RAID 5 volume in approximately 30 seconds. (Creating the partition and formatting the drive will take additional time.)
Volumes are created using an excellent wizard-based utility, which asks the right questions and guides inexperienced admins past the usual pitfalls, such as not leaving room on a partition for snapshots. In addition, nothing is set in stone with this system because volumes can be expanded or contracted on the fly, without disrupting user access, let alone requiring a reformat of the volume.
You can even add drives to an existing volume if you have prepared for it, using what Compellent calls Dynamic Capacity. This feature allows you to create a virtual volume that exceeds the current physical capacity of the system. When you add more drives later, you can allocate them to the existing partition without interrupting access to data.
Through use of Compellent’s virtualization service, Storage Center Core, volumes can also span multiple storage units, as well as different types of drives. This means that all the drives in a volume aren’t required to be the same size or brand, as most other systems require. I also found that changing RAID levels -- from RAID 10 to RAID 5 to RAID 1 -- can be done on the fly, without disrupting user access.
An unusual feature is what Compellent calls Data Instant Replay. This allows admins to schedule regular captures of changing data files and to map the capture, or replay it, to another drive letter or even a different server. If a user accidentally deletes a file or erroneously overwrites an existing file, the administrator can point the user to a copy of the appropriate version of the file. The process is intuitive, very fast, and puts most of the recovery operation in the hands of end-users.
The Compellent QuickStart systems are expensive and represent the high end of this roundup, but they’re also the most capable, offering extensive storage management features, great performance, and incredibly fast setup of RAID volumes. The monitoring tools are also excellent, showing historical trends in data access, wait times, and more, which allows for easy diagnosis of storage problems.
The Dell/EMC AX100 is a starter kit for FC SANs that comes with two QLogic HBAs, a Brocade SilkWorm 3250 eight-port FC switch, and a storage subsystem that supports dual controllers and as many as 12 SATA drives. The dual-controller configuration requires a dedicated UPS, which is also included. The UPS backs up the cache, ensuring that data is preserved even in a power outage. The configuration I received had eight 250GB drives; dual controllers; mirrored, dual redundant cache; redundant power supplies; the UPS; the Brocade switch; and all the necessary FC cable and software.
The AX100 storage subsystem is a full-featured enterprise enclosure with two dual-port FC controllers, redundant power supplies, and network connections for out-of-band setup and administration. The EMC Navisphere Storage System Initialization software automatically discovers the AX100 and performs basic configuration, while the Navisphere Server Utility allows for the easy configuration of snapshots and access to snapshots. Configuring the SilkWorm switch is similarly straightforward.
Installing the AX100 is a simple matter of installing the HBAs in the server or servers, making all the appropriate connections, and powering up the system. You then run the Initialization and Server Utility software, both of which are very straightforward. Finally, you can configure the storage array itself using a Web browser. The browser application works well and the interface is easy to navigate.
Setting up the storage system is simple enough, although there is one oddity: The subsystem OS resides on disks 0, 1, 2, and 3, so those disks already have small partitions on them. As a result, creating a disk pool that includes those four disks plus others isn’t recommended. Users who want to set up a single, large partition can do this, but the system will warn you it’s not a good idea. There are a number of places where the system will tell you if you’re doing something potentially dangerous. For instance, if you use all the disks to create a disk pool, the system will warn you that you should have a hot spare. You can always go ahead anyway, but the prompts help less experienced administrators stay out of trouble.
After you have created disk pools, you can create virtual disks, which are presented by the controller to the OS as a single attached hard drive. The difference is that you can resize a virtual disk if you have unallocated space on the AX100.
In addition to creating storage and managing it, the browser interface allows you to configure alerts, and it shows the status of the array and associated hardware, including power supplies, fans, and drives. One small irritant is that there is no power switch on the system, which can be powered off only by unplugging the unit.
The Dell/EMC AX100 is an excellent starter kit. For less than $10,000 (starting price), you get a complete SAN that includes solid redundancy, good storage management software, and a migration path to the EMC CX enterprise-class arrays.
DNF IPBank-E 1600
A relatively small company, Dynamic Network Factory is not nearly as well-known as Dell, EMC, HP, or IBM, but it offers solid storage management features and a good value in terms of gigabytes per dollar. An iSCSI storage system running Windows Server 2003 and FalconStor’s IPStor, the IPBank-E offers snapshots; Windows Volume Shadow Copy; mirroring; clustering, using mirrored or remotely replicated IPBank appliances; disk-to-disk backup; and virtual disks for on-the-fly expansion of volumes.
The IPBank-E 1600 is a 3U server with 16 drive bays and lots of room for expansion. According to DNF, the system will support as many as eight 10Gbps iSCSI HBAs, each of which can support as much as 8Gbps of true throughput. Other adapter options include multiple 1Gbps iSCSI, FC, and InfiniBand HBAs.
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