Dell/EMC's iSCSI AX100i makes storage networking easy and affordable but slow
If any technology is transforming from budget buster into budget saver, it’s storage area networks. Just a few years ago the cost per gigabyte of SAN storage and the expertise necessary to implement a SAN far exceeded the resources of small and even midsize businesses.
That has changed dramatically thanks to SATA, iSCSI, and the no-brainer setup software some vendors have begun including with their SAN hardware. Today, you can get a terabyte of networked storage for less than $10,000, and the capabilities of the included management software can be astonishing. For a sample of what’s available, see our January roundup of starter SANs.
One of the solutions evaluated in that test was the Dell/EMC AX100, a complete entry-level SAN kit combining SATA
drives, an FC (Fibre Channel switch, HBAs, a UPS, cabling, and smooth setup and management software from EMC. Now comes the AX100i, a low-end iSCSI SAN solution built on the same framework. The AX100i is identical to the original AX100 with the obvious exception of the iSCSI ports on the SPs (service processors). With a top-end capacity of 3TB in the form of twelve 250GB SATA drives, the AX100i can scale to suit any small-business application. The iSCSI interfaces permit smaller shops to use standard gigabit network interfaces in their servers as iSCSI ports (with software initiators) and gigabit copper network switches in lieu of expensive FC HBAs and fabric switches — further lowering the overall cost of the solution. The performance won’t measure up to an FC SAN, but if centralized, highly available storage is the goal, then top-notch performance isn’t necessary.
As with the original AX100, the target of the AX100i is the SAN novice. With little hassle, a SAN newbie should be able to deploy the AX100i within the space of one day. In fact, when the AX100i array arrived from Dell, I was able to configure and deploy the AX100i to a Linux and Windows server within one hour — even without the full manual, which Dell forgot to ship with my evaluation unit. Granted, I’ve been around iSCSI and FC SANs for awhile, but it really is easy.
EMC’s Navisphere Array Initialization application sets up the AX100i, requiring that the host system have a network interface on the same physical segment as the management ports of the AX100i’s SPs. Once the array has been discovered, authentication and IP parameters can be configured for a permanent deployment. Following this, the AX100i’s management is handled through the Navisphere Express Web console running on the AX100i. The initial configuration was as simple as it could be.
Defining arrays and virtual disks is equally straightforward. You select the physical disks from a representative layout grid, define the array parameters such as stripe size, and you’re done. You can then create virtual disks of variable sizes and bind them to specific hosts for proper presentation. You can just as easily expand virtual disks within the boundaries of the array.
I did, however, run into a problem with the initial array configuration. When the test unit first powered up, the second SP was unavailable for configuration. Although the SP was present and pingable, I could not change the IP and subnet assigned to its iSCSI port. After I stepped through the remediation procedure provided by Dell, this SP simply would not perform properly, except with a host attached. When Dell sent another unit, the new one initially exhibited the same behavior, but resetting it did somehow solve the problem.
Each server connecting to the AX100i must be configured with an iSCSI HBA or a software iSCSI initiator, and the Navisphere server configuration application must be run on the server to associate the server with the array. Both of these steps went without a hitch on Windows Server 2003 and on Linux. Although Dell does not officially support Linux hosts on the AX100i, they are perfectly compatible. In fact, the management CD shipped with the array contains the required initialization and server management applications for Linux.
Need for speed
On the Windows side, mounting SAN volumes on a server with redundant paths to the array requires EMC’s PowerPath. This is standard operating procedure, and presented no surprises. The Windows server accepted a single path to the SAN, and PowerPath held down the redundant path as expected. The AX100i can support eight servers with redundant paths, for a total of 16 connections. You can easily implement snapshot features for quick data recovery.
Unfortunately, the ease of installation and configuration of the AX100i comes at a price. Features you would expect to see in any iSCSI SAN solution -- jumbo frame support and flowcontrol settings on iSCSI ports -- are MIA. Nowhere within the Navisphere Express console were these settings available for inspection or modification. These controls can have a significant impact on the performance of an iSCSI SAN. In the case of the AX100i, their absence crippled SAN performance.
Ping tests showed the iSCSI ports unable to handle packet sizes larger than 432 bytes, bringing median performance of the array to between 30MBps and 40MBps on both Windows and Linux. (I tested the SAN using software iSCSI initiators and a Dell PowerConnect 5524 gigabit switch with jumbo frames enabled.) Dell claims that the next revision of the AX100i will include jumbo-frame support. That should bring a significant performance boost to this array.
Today, however, the AX100i delivers a level of performance comparable to many simple NAS devices, but nothing close to a well-implemented SAN. As a result, it’s frankly unsuitable for high I/O applications, such as Microsoft Exchange or SQL databases. You might use it effectively for tasks with lighter performance requirements, such as data archiving and file server storage -- but for applications requiring consistently fast access to volumes, you should look elsewhere.
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