SATA: Low-Cost Archival Storage

In an age of cost cutting, storage vendors are continuously on the lookout
for technologies that will reduce the overall Total Cost of Ownership (TCO) of
the company, although the cost of storage per byte is coming down. While network
storage technologies such as Storage Attached Network (SAN) and Network Attached
Storage (NAS) have considerably helped enterprises solve a lot of storage
related issues, storage is still looked upon as a cost factor.

This is because CFOs find it difficult to create charge-backs for different
departments that use the storage systems. Hence they are constantly on the look
out for more affordable storage systems and technologies that will address most
of their storage needs.

Off late, SerialATA (SATA) is gaining precedence as compared to parallel ATA.

SATA'S STRENGTHS

SATA eliminates the deficiencies present in ATA. It sends data serially rather
than in parallel, as conventional ATA does, thus replacing the cumbersome flat,
ribbon-cable with a slim, round, flexible cable that can be used in lengths up
to one meter.

Besides increasing the flexibility and doubling the length of the cable run,
SATA drive interfaces are simpler and smaller, and consume less power (and thus
produce less heat).

While SATA represents a breakthrough in hard drive technology, it requires a
lot of reliability testing to provide the utmost reliability and data protection
while being simple to use. After such issues are sorted out, SATA is poised to
grow phenomenally.

Gartner Research predicts a complete market switch from parallel to SATA
disks over the next year. By 2005, analysts expect 300 million SATA disks to
ship into the marketplace, annually.

READ AFTER WRITE MECHANISM

For SATA to be used as a successful enterprise storage technology, vendors
have to introduce new features that safeguard data integrity, enhance data
protection, and reduce drive failure rates dramatically: read-after-write,
increased sparing, and surface-cleaning logic. By incorporating these features,
SATA intermixes options with enterprise class storage systems to provide
organizations with a low cost and highly reliable archival storage platform.

However, for SATA drives to become commercially viable for enterprise
storage, few aspects should be kept in mind. The data protection systems that
need to be deployed in storage systems employing SATA drives, should incorporate
a 'read-after-write' mechanism.

As the lower cost drive bearings and motors used in SATA technologies wear
over an extended period of usage, the disk heads may begin to misalign with the
tracks on the disk. Consequently, data can be written onto the disk that cannot
be read back.

To watch for such wear, a controller needs to be put in place so that it
keeps a copy of the original data in cache memory as it writes that data onto
the disk. The controller then physically rereads that data into cache memory and
uses 'Verify' byte check logic borrowed from the SCSI command set to make
sure the correct data has been recorded.

Steps should be taken to maximize the efficiency, availability, and
implementation of disk spares in storage systems that use SATA. Organizations
need to prioritize the rebuild function over host I/O in the portion of storage
systems that use SATA drives. In systems using drives designed for continuous
production workloads, one has to prioritize host I/O so that the user sees no
performance degradation while the system is rebuilding a failed drive.

RECORD ENVIRONMENTAL CONDITIONS

Further, it is a win-win situation for organizations that already have a
storage system in place, while they get the option of deploying a fixed-content
archival storage system based on a SATA drive that integrates seamlessly with
primary storage for operational data. Moreover, if it can be managed using the
existing storage management solution, it represents a true data lifecycle
strategy for enterprise data assets.

Lim Beng Lay is Product
Manager, Asia-South for Hitachi Data Systems.