It takes a massive double enclosure to house the UDSS DiskArray from Legacy Storage Systems
(www.legacy.ca). The size of two standard PC towers
standing side-by-side, this unit houses dual
RAID controllers, four power supplies and 14 Seagate hard drives connected to three internal Ultra
SCSI busses.
UDSS DiskArray
Legacy Storage Systems Corp.
Markham, Ontario, Canada 905-475-1077 Description: External RAID Subsystem with dual (hot swappable) RAID controllers Cache: 64 Mbytes (mirrored) Interface to host: 2 X Ultra SCSI, 2 X Ultra2 SCSI Interface to drives: 3 X Ultra SCSI Enclosure: 16 drive bays (2 occupied by RAID controllers), four hot swappable power supplies (two for each half of the enclosure), dual cooling systems Performance ·Cache test: 100 commands per second, 26 Mbytes/sec. ·Transaction rate: ~500 per second ·Throughput: 25 Mbytes/sec. Advantages: Very fast transaction rate, excellent for database operations. Platform agnostic — set up with just terminal software. Disadvantages: Throughput may not be high enough for large docs, CAD files, complex images and other large files. Price: $17,500
This externally controlled RAID system appears to your server as an ordinary, albeit
large, hard drive, and provides plenty of flexibility. The four SCSI host interfaces can be connected
to a single server with four SCSI connections or to separate servers clustered together. There is a
serial port available to connect the RAID to a terminal or PC running terminal software.
The dual
array case has a total of 16 slots (8 per side), but since the controllers take a single slot each, 14
slots are available. Up to eight separate RAID arrays can be set up on the DiskArray. Each can be
partitioned off and assigned its own SCSI ID number for separate servers. Partitions can be assigned
to more than one host interface for server clustering.
The unit came installed with 14 9-GB Seagate
drives. Six drives were arranged as a Level 5 array with one spare drive on one SCSI channel. The
other eight drives were arranged as a Level 5 array with one spare drive on two SCSI channels (four
drives per channel). Spare drives can also be set up globally — that is they can fill in for any
failed drive and don’t have to be attached to any particular array.
In our tests, we set the system up with a PC using the Hyperterminal software included with Windows.
The setup computer doesn’t have to be the machine accessing the RAID subsystem, so a system
administrator can use a portable computer to setup several DiskArrays spread throughout a building. If
you don't like terminal software, Legacy includes software called GUI RAID Manager. You can use
it to administer the RAID either through its serial port or remotely over Ethernet using simple
network management protocol (SNMP).
Our test bed was a 600 Mhz Pentium III computer running Windows NT 4.0 (Service pack 4) with an
Adaptec Ultra2-LVD SCSI host adapter. Preliminary tests showed a transaction rate of 100 I/Os per
second and throughput of 26 Mbytes/sec. when accessing just the cache.
In a second round of tests, I/O rates reached more than 500 I/Os per second with 2-kilobyte transfers
simulating database operations. More importantly, the initial burst of transactions was twice as high,
the result of having a large and fast cache in the controllers.
With 10-kyte files (simulating a typical compressed document image), transfer rates were about 340
I/Os per second. When we switched to large, 2-Mbyte transfers, the best throughput was about 25
Mbytes/sec.
This performance suits the Legacy UDSS DiskArray for high-transaction-rate environments or use with
small (1-2K) files. It would be less well suited to high throughput environments with larger files.
The front of the array is protected by two removable plastic doors, each of which is fixed in place by
a lock. There is no master power switch. Instead, each power supply is independently switched in the
back of the unit and in the front of the unit. Since the DiskARRAY is essentially two separate
enclosures that have been attached, the power supplies operate in pairs. If both power supplies are
turned off in the right-hand enclosure, it shuts down. Therefore, the power supplies have only dual
redundancy.
