Networking World: Why will you like SAS?

NETWORK WORLD NEWSLETTER: MIKE KARP ON STORAGE IN THE ENTERPRISE
06/30/05
Today's focus: Why will you like SAS?

Dear networking.world@gmail.com,

In this issue:

* A coming out party for Serial Attach SCSI
* Links related to Storage in the Enterprise
* Featured reader resource
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FOCUS ON RECOVERY

Today's focus: Why will you like SAS?

By Mike Karp

In San Jose last week, Bell Micro, Fujitsu, LSI Logic and
Supermicro got together to hold a coming out party for Serial
Attach SCSI, or SAS, the newest incarnation of the SCSI device
interface.

The offering comes from Bell Micro, which is bundling Fujitsu's
2.5-inch SAS disk drives and LSI's SAS host bus adapters inside
eight-bay device canisters from Supermicro. Bell expects the
package to appeal to the channel, primarily going into direct
attach configurations that require access to lots of data along
with high-speed I/O.

The SAS interface offers several advantages. Most obvious is the
significant improvement over parallel SCSI when it comes to
throughput (about four times the capacity). SAS also allows many
more drives to be connected to the SCSI bus: parallel SCSI had
room for devices at 15 addresses, but even assuming multiple
logical units (LUN) at each address, parallel SCSI could never
approach the connectivity that SAS allows - up to 128 addresses
using an expander.

Of course, neither parallel SCSI nor serial SCSI could ever
access data from so many devices at once - five devices
operating at the same time is a number likely to saturate the
bus. Still, with proper management, an application can be
connected to a lot of data using SAS and then streamed in as
appropriate.

Vendors like serial technologies because they are substantially
easier to design for than parallel connections. Serial
technologies require less bulk when it comes to cabling cable
(that means lower costs), and less bulk means less-restricted
air flow and thus smaller fans (cheaper again). But the main
reason vendors like designing for serial is that the
relationship of signals and the system clock is again much
simpler. For example, parallel SCSI has to coordinate clock
ticks with signals along multiple separate parallel wires but
with SAS, all signals travel along a single wire. Controlling
timing is easier, and device back planes, connectors, and so
forth are easier to design. Oh yes, and cheaper to design as
well.

But why will you like SAS? Glad you asked.

Engineers probably think you will like it because it maintains
(and extends) the same rich command syntax for manipulating data
that SCSI has been using for two decades, while at the same time
providing for much faster data transfer rates.

I say you'll like SAS because it goes a long way towards putting
you back in control of your storage budgets. Here's why.

The SAS backplane offers you several very nice advantages. One
you will get a lot of mileage from is the fact that with a SAS
backplane you can plug in either SAS or Serial ATA (SATA)
devices. SATA devices will be significantly cheaper than SAS,
and in many cases will provide perfectly acceptable performance
and reliability. For "nearline" operations such as second-tier
storage or use in a virtual tape library, they will certainly be
just fine. Many smaller shops that are very price-sensitive will
go with them for almost all their storage needs.

But it is important to bear in mind that the SAS devices are
tested against a much more rigorous standard than are the SATA
drives. Mean time between failure (MTBF) and the duty cycle
against which SAS devices are tested distance them from the SATA
devices: thus, expect them to last longer and to take more of a
beating. For many IT managers this will be an important
differentiator.

Also, SAS drives come with a second data port to support
redundant data path configurations. Because of this, you can
assume that not only are the drives themselves more robust, but
because they also provide twice as many data pathways, they
supply a higher availability system when the data leaves the
drive.

The important point to keep in mind is that you can play mix and
match within a device - one bay of drives can be SAS, the next
can be SATA, and so forth. You can make your decision on
populating with SAS or SATA based on need and economics, and not
because you are locked-in to a particularly technology.

Looked at individually, SAS and SATA each offer significant
benefits. Taken together, they supply an excellent choice for
you as you look to your next round of storage buys.
_______________________________________________________________
To contact: Mike Karp

Mike Karp is senior analyst with Enterprise Management
Associates, focusing on storage, storage management and the
methodology that brings these issues into the marketplace. He
has spent more than 20 years in storage, systems management and
telecommunications. Mike can be reached via e-mail
<mailto:mkarp@enterprisemanagement.com>.
_______________________________________________________________
This newsletter is sponsored by Oracle
Boost the quantity and quality of customer interactions!

How can companies get a fuller, sharper picture of their
customers to boost the quantity and quality of customer
interactions? By creating a standardized customer-data model via
an "information grid." IDC analyst Stephen Hendrick explains how
to achieve a "360-degree view" of customers for better selling
and marketing.
http://www.fattail.com/redir/redirect.asp?CID=107445
_______________________________________________________________
ARCHIVE LINKS

Archive of the Storage newsletter:
http://www.networkworld.com/newsletters/stor/index.html

Breaking storage news and analysis:
http://www.networkworld.com/topics/storage.html
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Best practices for implementing a virtualization platform

Join IDC analyst, Dan Kusnetzky for a look at the benefits of
virtualization and how IT departments can use software to
consolidate servers, optimize software development, and enable
affordable business continuity.
http://www.fattail.com/redir/redirect.asp?CID=107334
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FEATURED READER RESOURCE
FOCUS ON RECOVERY

IT professionals are changing the way they back up and recover
data, experts say, with new emphasis on the speedier fetching of
data made possible by advancing technologies. At a recent
storage conference in Orlando, disk-based backup solutions were
touted - find out if attendees agreed and if faster storage
solutions will soon be available. Click here:
<http://www.networkworld.com/news/2005/062005-data-recovery.html>
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Networking World

Thursday, June 30, 2005

Why will you like SAS?

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