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STORAGE INSIDER: MARIO APICELLA                 http://www.infoworld.com
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Tuesday, August 17, 2004

A SOPHISTICATED STORAGE PALATE

By Mario Apicella

Posted August 13, 2004 3:00 PM Pacific Time

How to better use new technologies is one of the most debated topics in
the storage world, which is not surprising because often a new
technology opens doors that were previously locked and forces potential
users to walk away from the familiar beaten path.

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Take, for example, desktop-grade SATA (serial ATA) drives. Many people
are understandably confused by these drives that seem to have grown too
big for their breeches and dare to invade the sacred sphere of
enterprise deployment.

RAID solutions that deploy low-cost SATA drives are becoming quite
common, although it's fair to say that similar configurations based on
parallel ATA drives have never been that popular.

However, SATA deployments in that context have not always been smooth,
according to Hubbert Smith, director of marketing for enterprise
products at Western Digital.

Customers were noticing some erratic behavior when deploying Western
Digital's 250GB Caviar drives in demanding RAID environments, Smith
explains. That erratic behavior included drives that, when under heavy
load, stopped responding, or drives that spent too much time on error
recovery.

Similar incidents are bad enough when they affect single drives, but on
RAID configurations those errors can spell disaster. For example, if a
drive remains uncommunicative for a long time, its RAID controller can
misinterpret that busy status as an unrecoverable disk failure and
(assuming that a spare drive is available) may start rebuilding the
array.

If this doesn't sound too bad, let me remind you that rebuilding a 250GB
drive in RAID 5 can take several days (yes, several 24-hour cycles).
Concurrent data access is still possible during rebuild, but if another
drive fails or becomes unresponsive -- a strong possibility given that
drives are working overtime -- you can kiss your data goodbye for good.

Considering that quite possibly nothing was actually wrong to start
with, calling this behavior a catastrophe is perhaps too mellow a
euphemism.

Should we take this as a lesson to never deploy those drives in a RAID
array?  Not necessarily, according to Smith. Western Digital engineers
came up with 26 improvements that the company consolidated into a new
product line named Caviar RE (RAID Edition).

The most apparent improvement of the new line is that the mean time
between failures is now a healthy 1 million hours, which should
drastically reduce the possibility of errors, and therefore the time
spent on error recovery.

In addition, a busy Caviar RE drive won't just fall off the RAID
controller screen, but will maintain communication, which should
eliminate the main cause for "apparent" drive failure and unnecessary
rebuilds.

Western Digital suggests that the Caviar RE drives, which cost only a
few dollars more and are available in several capacities both with SATA
and EIDE (Enhanced IDE) interfaces, are a good compromise between cost
and reliability for applications that are not business-critical, such as
video surveillance, backups, and file and e-mail servers.

In today's sophisticated storage world, those names may mean different
things to different customers, but one thing is for sure: SATA drives
have now acquired another possible classification layer that could
confuse the unsuspecting.

Mario Apicella is a senior analyst at the InfoWorld Test Center.




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