Mylex DAC960PG, Installation Manual

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Controller Components
2-4 DAC960PG Installation Guide
Ultra-SCSI Bus Interface
The three Ultra-SCSI channels can be simultaneously accessed by dedicated
BA81C15 PCI to Ultra-SCSI ASICs. Each channel supports up to 15
physical SCSI drives. The DAC960PG supports Wide Ultra-SCSI as well as
earlier SCSI standards. The DAC960PG delivers SCSI data transfer rates up
to 40 MB per second per channel.
Configuration on Disk
Firmware 4.x provides Configuration on Disk (COD). COD allows a RAID
equipped computer to detect certain hardware changes when they occur, and
automatically reconfigure accordingly. Automatic reconfiguration occurs
after hardware changes such as:
• Change of controller card in the event of a controller failure, or if a
controller with more channels is needed
• Change of target IDs (relocating drives) or replacement of drives
• Interchange of cables
The configuration information is stored in the last 128 sectors of every
working physical hard disk This area is reserved by Mylex for this purpose.
Management of Bad Data
Firmware 4.x supports the handling of data that cannot be reconstructed at
the time of a rebuild. A Bad Data Table is maintained in memory. Whenever
a change is made to the table, the table is saved on all disks in the
configuration.
Bad Data Table entries are made during the rebuild and add capacity
processes. If a bad sector is encountered, a sector-by-sector scan is initiated
on the stripe in which the error occurred. The corresponding system sector
number is inserted into the Bad Data Table, and the sector is immediately
overwritten with an arbitrarily selected pattern, making it invalid for reading.
Subsequent read operations check the Bad Data Table to determine whether
any of the blocks about to be read are bad data blocks. If this is the case, an
error condition is returned.
Subsequent write operations check the Bad Data Table to determine whether
any of the blocks about to be overwritten are bad data blocks. If this is the
case, the blocks are deleted from the Bad Data Table and the data is written
to the disk.