HP Xw8200 LSI SCSI: Integrated RAID User's Guide (PCI plug-in and system board - Page 21

Media Verification, SCSI ID Assignment, Disk Write Caching, NVSRAM Usage

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2.4.7 Media Verification The IM firmware supports a background media verification feature that runs once per minute when the IM volume is in optimal mode. The media verification feature issues a SCSI Verify command to a segment of the disk. If the command fails for any reason, the other disk's data for this segment is read and written to the failing disk in an attempt to refresh the data. The current Media Verification Logical Block Address is written to non-volatile memory occasionally to allow Media Verification to continue approximately where it left off prior to a power-cycle. 2.4.8 SCSI ID Assignment A single logical drive is presented as the combination of a set of physical member disks. Each individual member disk is hidden and returns a "selection timeout" when accessed. The SCSI Target ID of the IM logical drive is assigned when the logical drive is created. The lowest SCSI ID of the selected disks is used. 2.4.9 Disk Write Caching The IM firmware disables disk write caching. This is done to increase data integrity, so that the disk write log stored in NVSRAM is always valid. If disk write caching were enabled (not recommended), the disk write log could be invalid. 2.4.10 NVSRAM Usage IM firmware requires a 32 Kbyte NVSRAM in order to perform write journaling. Write journaling is used to verify that the mirrored disks in the IM volume are synchronized with each other. The NVSRAM also stores additional code and data used for error and exception handling, and it stores IM configuration information during serial EEPROM updates. The disk write log uses approximately 4 Kbytes of the NVSRAM. Integrated Mirroring Firmware 2-7 Version 1.0 Copyright © 2003 by LSI Logic Corporation. All rights reserved.

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Integrated Mirroring Firmware
2-7
Version 1.0
Copyright © 2003 by LSI Logic Corporation. All rights reserved.
2.4.7
Media Verification
The IM firmware supports a background
media verification feature
that
runs once per minute when the IM volume is in optimal mode. The media
verification feature issues a SCSI Verify command to a segment of the
disk. If the command fails for any reason, the other disk’s data for this
segment is read and written to the failing disk in an attempt to refresh
the data. The current Media Verification Logical Block Address is written
to non-volatile memory occasionally to allow Media Verification to
continue approximately where it left off prior to a power-cycle.
2.4.8
SCSI ID Assignment
A single logical drive is presented as the combination of a set of physical
member disks. Each individual member disk is hidden and returns a
“selection timeout” when accessed. The SCSI Target ID of the IM logical
drive is assigned when the logical drive is created. The lowest SCSI ID
of the selected disks is used.
2.4.9
Disk Write Caching
The IM firmware disables disk write caching. This is done to increase
data integrity, so that the disk write log stored in NVSRAM is always
valid. If disk write caching were enabled (not recommended), the disk
write log could be invalid.
2.4.10
NVSRAM Usage
IM firmware requires a 32 Kbyte NVSRAM in order to perform write
journaling. Write journaling is used to verify that the mirrored disks in the
IM volume are synchronized with each other. The NVSRAM also stores
additional code and data used for error and exception handling, and it
stores IM configuration information during serial EEPROM updates. The
disk write log uses approximately 4 Kbytes of the NVSRAM.