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DRAM and flash configuration
The V6SSD can be configured with or without DRAM, with or without flash memory.
A flash-only unit can serve as a write-protected boot device or a non-volatile data
storage drive. A DRAM-only unit is a volatile, ultra-fast storage device used to record
large amounts of data or to optimize data base operations. With both flash memory and
DRAM, it can address all of these applications. Start with up to 1GB of flash memory on
the VME baseboard and stack up to two 1GB DRAM mezzanine cards in a single VME slot or
four mezzanines in a double-wide slot.
The V6SSD can be addressed as a single or dual
logical unit number (LUN). There are three modes of operation. The one most appropriate
for an application depends on whether or not flash is to be write-protected.
Mode 1: one LUN, write-enabled flash memory
If the host does not support multiple SCSI LUNs, the user partitions the drive between
the non-volatile flash section and the volatile DRAM section. Writes to flash are first
written to DRAM cache then retired to flash after one minute (five minutes for frequently
updated sectors) or by issuing a SCSI "stop" unit command. Subsequent reads of
updated sectors come from this cache rather than flash. This buffering feature speeds up
flash accesses and reduces excessive wear on the flash memory.
Mode 2: two LUNs, write-protected flash memory
If the host supports multiple SCSI LUNs, one LUN is assigned to the non-volatile flash
memory and the other LUN to volatile DRAM. After the operating system is committed to
flash memory, that LUN can be write-protected with the front panel switch.
Mode 3: one shadowed LUN, write-protected flash memory
For operating systems, such as Solaris, which attempt to write to the same LUN it boots
from, the flash is configured as a shadowed LUN of the DRAM. The first time a flash sector
is read by the host, it is also copied to the corresponding DRAM sector. Since subsequent
reads and writes are directed to DRAM, the flash is naturally write-protected. The OS is
committed to flash by configuring the system and issuing a specific SCSI or RS232 command
which copies only sectors written in DRAM to the flash memory. Although the number of DRAM
sectors determines the size of drive, the flash size must be large enough to store all
written sectors of DRAM.
SCSI Interface
Two single-ended SCSI interfaces are available on the V6SSD. A SCSI-2 (8-bit
narrow, max of 10MB/sec) on the VME’s P2 connector is compatible with the Force and
Themis CPUs. A 68-pin SCSI port (16-bit wide, 20MB/sec) with pass-through is accessible
via ribbon cable on the front panel. A differential SCSI option will soon be available on
the front panel interface.
The SCSI ID is set by rotary switches; one for the interface via front panel and one
for the VME P2 bus. Jumper selectable options can terminate either SCSI interface. Power
is supplied for the terminator.
Software transparent
No modifications to the host software or device drivers are required.
Wear-leveling flash memory
Write to flash memory first goes through DRAM cache on the baseboard. Each
time a sector in flash memory is updated, it is logically replaced by the
"least-used" sector to avoid excessive writes to any one flash sector. During
periods of inactivity, the V6SSD relocates data from highly used to least used sectors.
These procedures are transparent to the host computer.
Error detection/correction
Single-bit DRAM and flash memory errors are automatically detected and
corrected through the CRC/ECC method. Seven percent of available memory is allocated as
bad sector spares for replacement of blocks with excessive errors. Double-bit errors are
detected and reported.
Quick format
A snapshot of the non-blank areas of the DRAM following formatting and
directory structuring is compressed and stored in a reserved 8MB of flash on the DRAM
mezzanine. This is used to format the drive on power up. During
power-up, the snapshot is automatically expanded into DRAM to format the drive. A minimum
of 64MB of flash memory is provided on the V6SSD baseboards. This is adequate to restore
any conceivable formatting and initial directory structure.
Status indicators
Three front panel bi-colored LED status indicators
- front panel SCSI activity
- P2 SCSI activity
- array processor activity
Quick erase
The contents of the storage device can be quickly erased by a manual switch, a
RS232 or SCSI command. The manual switch can be a front panel toggle switch or a remote
dry contact switch interfaced to the VME’s P2 connector. User-selectable patterns
downloaded from the host are used to sanitize all DRAM and its FIFO buffer. Flash memory
is erased by all ones. During this scrubbing, the device will not be accessibly by the
host. When the erase is complete, the V6SSD will be restored to the power-up state,
requiring a reboot of the host computer. This procedure takes less than one minute for all
DRAM and two minutes for 1GB of flash memory.
Diagnostics
Software is supplied to identify defective components by using the RS232 port
(P2 access).
Battery backup
Two pins on the P1/P2 connector are made available to provide battery backup.
The DRAM is automatically refreshed when in standby mode.
Firmware updates
Feature enhancements and bug fixes are available on our web site and can be
downloaded to the V6SSD’s firmware over either the SCSI port or the RS232. The source
of the utility to download the firmware is supplied with the unit and has been tested with
Sun OS, Solaris, Windows 95 and NT.
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