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Another approach to self-healing storage

Over the last several weeks, I’ve been writing about the self-healing storage arrays announced by startup Atrato Inc. and a more seasoned company, Xiotech Corp. Seeing this, another company stuck its hand up to say, “Hey, we have that too!”

This other company is Data Direct Networks, and their self-healing product has actually been on the market in one form or another for some time now (DDN has been in business 10 years), but I wasn’t aware of it until they got my attention last week.

DDN’s product line consists of four hardware models: the S2A6620, 9550, 9700 and 9900. The self-healing stuff resides mostly in the S2A operating system. Like BlueArc’s Titan NAS heads, DDN’s products put some of the heavy-duty processing of data, such as parity calculations, into silicon by way of field-programmable gate arrays (FPGAs). According to DDN’s CTO Dave Fellinger, this, along with parallelization, means that the arrays can write and read at the same rate.

What that sets up is the ability to calculate two-disk parity on every read, as well as every write, without performance degradation. So theoretically the system never goes into rebuild mode, because it already operates in that mode all the time.

Like the systems from Xiotech and Atrato, DDN’s systems perform disk scrubbing, as well as isolation of failed disks for diagnosis and attempted repair. The product can conduct low-level formatting of drives, power-cycle individual drives if they become unresponsive, correct data using checksums on the fly if it comes off the disk corrupt, rewrite corrected data back to the disk, and use S.M.A.R.T. diagnostics on SATA disks to determine if the drives need to be replaced. (Atrato also uses S.M.A.R.T., among other error correction codes.)

The key difference between the DDN product and the others is that DDN’s disk arrays are not sealed. According to Fellinger, the company’s experience in large environments suggests that sealed arrays are impractical.According to Fellinger, the company’s experience in large environments suggests that sealed arrays are impractical. So admins swap out individual drives at DDN installations, the largest of which is an 8 PB deployment at Lawrence Livermore National Labs.

However, it seems Xiotech and Atrato are going after slightly different markets than DDN. Each of those vendors talks in capacities of 16 TB and 3U rack units. Xiotech said it is specifically going after enterprise accounts with its ISE system; Atrato seems to be targeting a more similar market to DDN in multimedia and entertainment. DDN claims to already have the big fish, such as AOL/Time Warner, locked up. And, Fellinger added, the company has just released an entry-level system with 60 drives offering up to 2 GBps performance.

For me, anyway, an already interesting and (relatively) new market just got that much more intriguing.

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