computerworld.com
New tools juggle access to disks
Middleware lets servers see only assigned storage
By Nancy Dillon
03/22/99 As many information technology managers have learned, it's
difficult to maintain lines drawn in a SAN.
That's especially true if the storage-area network (SAN) includes
Windows NT.
"If you bring up a raw SAN and hook up all of your NT servers, each will
try to claim all of the disk. Then when one tries to write something,
the rest go bonkers [with error messages]. NT just doesn't play nice
when it comes to partitions," said Mark Hargrove, a network architect
for the United Space Alliance at the John F. Kennedy Space Center in
Cape Canaveral, Fla. His group handles all the processing that goes into
preparing for a space shuttle mission.
"Ideally, a SAN connects all servers to all storage" using a front-end
LAN as the paradigm, said Robert Gray, an analyst at International Data
Corp. in Framingham, Mass. SANs can improve server performance and data
availability by moving storage out of individual servers and onto a
high-speed network with multipath fail-over. But Gray said they can be a
nightmare if users don't find ways to introduce appropriate
restrictions.
"Every SAN will require some sort of access management," Gray said.
"Without it, rogue servers can get in and corrupt anything."
Several new software tools attempt to address that SAN access problem.
For example, Transoft Networks Inc. in Santa Barbara, Calif, transoftnetworks.com., released
SAN Manager last week. SAN Manager is middleware that can assign
different servers to the various logical unit numbers available on a
single storage connection. Logical unit numbers are a type of partition
that identifies a physical storage device or part of a storage device.
So even if directly connected to vast disk resources, a server only
"sees" the storage exclusively assigned to it. Unassigned storage is
"masked."
The software supports NT and Unix, works with Fibre Channel hubs and
switches and can dynamically reallocate logical unit numbers from a
central management console. Pricing starts at $7,495.
"[Logical unit numbers] masking is really what has been missing for me,"
said Hargrove, who's beta-testing SAN Manager. Hargrove is building a
SAN comprising six storage arrays, eight Fibre Channel switches, 12 NT
servers and six Unix servers.
"Before [logical unit numbers] masking, you had to dedicate an entire
storage processor port to one NT server. That got very expensive; my
dual-port processors are $35,000 each," Hargrove said. With SAN Manager,
he said, the same NT server can share a single port with multiple
servers using a hub or switch.
Other products that tackle the same sharing problem include Hopkinton,
Mass.-based EMC Corp.'s Volume Logix on the high end and Round Rock,
Texas-based Dell Computer Corp.'s new OpenManage Storage Consolidation
on the low end. But unlike SAN Manager, those products are tied to their
proprietary arrays. |
