StorGateTM
Storage Gateway
for VOS Continuum to EMC
Symmetrix DMX Connectivity
SCSI Model
Expanded Product Brief
The DRA StorgateTM Storage Gateway
is a drop-in solution which provides VOS Continuum hosts with seamless access to
VOS data on EMC Symmetrix DMX storage arrays.
StorGate meets all requirements for a
certified host. By using StorGate, Stratus VOS Continuum users
can store and retrieve VOS data on their existing storage arrays while
maintaining full support for their equipment.
Key Features
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Provides drop-in fully supported VOS-to-EMC
Symmetrix DMX connectivity
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Connects directly to DMX via Fibre Channel
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Connects directly to VOS Continuum via
K450/K460 SCSI ports
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Allows VOS to see DMX storage as
common VOS disk types (D706, D711, D712)
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Emulates VOS disks and disk trays - up to
12 virtual VOS disks per StorGate/RAID unit
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Stores VOS data directly in VOS file format
(Note: VOS does not support data sharing between hosts)
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Can be duplexed to standard Stratus VOS
disks or can be used in pairs for duplexing
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Meets or exceeds native
VOS disk performance in most applications (using DMX mirroring
with metavolumes)
Subsystem Overview
StorGate provides
a connection between a VOS Continuum BIO (K450/K460) port and DMX host
adapter port. StorGate "on-the-fly" disk emulation and
data translation capabilities allow VOS Continuum users to store and retrieve
data on a DMX just as if the data were stored on standard
Stratus disks.
Each StorGate unit provides access to up to 12
virtual VOS disk volumes on the DMX. Each of these virtual disks may be a
VOS D706, D711, or a D712 disk type. This means that each StorGate unit allows a VOS Continuum to access up to 408 GB (physical) on a
DMX storage array. Multiple
StorGate units may be attached
to multiple BIO ports on a single VOS Continuum host to provide access to as
much DMX storage capacity as desired, up to the maximum allowed by VOS
(3.2 TB logical, 6.4 TB physical). Multiple StorGate
units may also be used to allow multiple VOS Continuum hosts to access one or
more DMX storage arrays. (Although StorGate allows
multiple VOS hosts to store data on a single DMX, VOS limitations prevent
sharing that data between hosts.)
StorGate supports all VOS disk-related
commands and functions. It uses standard RAID hypers and metavolumes to store VOS data
on a DMX storage array. This allows the DMX to manage VOS virtual
disks as standard RAID storage volumes. Both mirrored and Raid-S volume types
are supported.
Physical Connections
A VOS Continuum host connects to StorGate
through a Continuum BIO (K450/K460) SCSI port. A DMX connects
to StorGate through a Fibre Channel port on a DMX Fibre Channel host adapter. (Refer
to the StorGate Technical Specifications for connection
details.)
StorGate provides a direct physical data path
between a VOS Continuum host and a DMX. In other words,
StorGate can be viewed as simply a "black box" between a VOS Continuum host and a
DMX. Data
transfer and disk emulation functions are performed transparently, "on the
fly," as data moves between VOS and the DMX. This allows a VOS Continuum
host to see StorGate as one or more standard Stratus disks, and
a DMX to see StorGate as a standard,
DMX-supported host.
Configuration Options
StorGate provides a variety of highly flexible
configuration options for access to the DMX from VOS Continuum
hosts. This flexibility arises from the unique way in which StorGate stores VOS data on the
DMX.
StorGate stores VOS data on the
DMX as one
or more virtual Stratus disks. VOS D706, D711, and D712 disk types are currently
supported. From the VOS host perspective these virtual disks behave identically
to physical VOS D706, D711, and D712 disks. In fact, these virtual disks match
so exactly to the equivalent Stratus physical disks that a virtual disk on the
DMX can be duplexed with an equivalent physical Stratus disk. This allows a
wide variety of possible configurations, some of which are illustrated below.
Many configurations are possible in addition to those shown
above. Please contact your Account Executive for questions regarding specific
configurations, or if the configuration you need is not shown above. The
StorGate configuration table is usually defined only once, at
installation time, by DRA. It does not need to be changed unless the DMX is
reconfigured.
Note that each physical connection between a
VOS Continuum host and the DMX requires one StorGate unit. This means that two
StorGate units are required to
provide true VOS duplexing between VOS virtual disks on the DMX.
Internal Operation
StorGate acts as a translator
between the VOS I/O subsystem and the DMX I/O host interface. This is
illustrated in the following diagram.
When a VOS application issues an I/O request ("s$"
call or programming language I/O function), the VOS I/O subsystem converts it to
a physical I/O command. The BIO (K450/K460) then passes this command to
StorGate over the Stratus SCSI bus.
StorGate responds to each VOS physical I/O
command exactly as a
standard Stratus disk (D706, D711, or D712) would respond. In order to
accomplish this disk emulation, StorGate converts the Stratus
disk address into an address for the corresponding data on the DMX, performs
the appropriate I/O operations on the DMX, then converts data and status
returned by the DMX into an appropriate response for the Stratus BIO
(K450/K460). This disk emulation is so exact, even at the hardware level, that
StorGate virtual disk volumes can be partnered with physical
Stratus disks in duplexed pairs.
Each StorGate can emulate either 1 or 2
Continuum disk trays, providing up to either 6 or 12 disk volumes in any
combination of supported disk types (D706, D711, or D712). Simple, table-driven
disk emulation allows new disk types to be supported quickly and easily.
Installation
StorGate connects directly into the data path
between a Stratus VOS Continuum host and a DMX. One
StorGate unit must be installed for each physical connection
between a VOS Continuum and a DMX. This means that each VOS duplexed connection requires two StorGate units, one for each
data path. The diagram below illustrates this point.
Each StorGate unit has four connectors on the
back: AC power, host data port, storage array data port, and Ethernet port.
These are illustrated in the photograph below.
The AC power connection accepts standard voltages and current
levels, as specified under Technical Specifications. If either the host
(Continuum) or the storage array (DMX) is connected to an uninterruptible
power supply (UPS) then each StorGate unit should be connected
to that same UPS.
The host data port provides a Stratus standard fast-wide SCSI
connection to a Continuum host. The connector is a standard HD-68 type which
accepts a cable from a VOS Continuum BIO (K450/K460) SCSI port. Direct
connection to a BIO (K450/K460) SCSI port is recommended for best performance.
StorGate uses DRA-provided cables (available from Stratus) for
connection between VOS Continuum hosts and StorGate.
The storage array data port provides a
Fibre Channel connection to the DMX.
Only one type of storage array data port is provided on each StorGate unit. The Fibre
Channel data port provides a standard domed duplex SC connector which accepts a
62.5 micron multimode fiber cable from the corresponding DMX Fibre Channel
host adapter port. The Fibre Channel data port may only be used for a single
direct FC-AL private loop connection between the StorGate Fibre Channel data
port and the corresponding DMX Fibre
Channel host adapter port. StorGate uses DMX-provided cables for connection
to DMX.
The Ethernet port is a standard RJ-45 10/100BaseT Ethernet
connector. This port provides TCP/IP communications capability for
diagnostic connections from the VOS host. It is not intended for any other
purpose.
Performance
Laboratory tests indicate that for many
applications StorGate provides throughput which equals or exceeds that of
equivalent Stratus disks. In these laboratory tests the best performance was
achieved when the virtual disks on the Target were configured as Target-specific
mirrored metavolumes. Performance in other environments may vary, and
depends upon a variety of factors. These factors include application data access
patterns, overall Target storage array configuration, and I/O activity by other
hosts attached to the Target storage array.
Product Support
DRA products purchased through Stratus
are supported jointly by DRA and Stratus. DRA products
purchased directly from DRA are supported through the Co-active Maintenance
Service (CMS). CMS is a total support agreement which is available "around
the clock, around the world" to participating DRA customers. Product
maintenance, product updates, documentation and training are available through
CMS support. CMS is provided free of charge for 90 days following product
installation, and may be extended by contract thereafter.
