IBM PC Server 520, Руководство пользователя

Страница: 139 / 438

Additional Disk-Array Tasks
Ÿ Read ahead — On
Normally, the ServeRAID adapter transfers data from disk to its
local cache in steps of stripe-unit size. This provides excellent
overall performance when workloads tend to be sequential.
However, if the workload is random and system I/O requests
are smaller than stripe-unit size, reading ahead to the end of the
stripe unit will result in a wasted SCSI bus bandwidth and
wasted disk utilization. When read-ahead is set to Off, the size
of data transfer from the disk to local cache is equal to the
system I/O request size, and no read-ahead to the end of the
stripe unit is performed.
Notes:
1. The read-ahead setting can be changed without
destroying data in a logical drive.
2. When the configuration is saved on a diskette, the RAID
parameters are saved also.
Unattended Mode of Operation
You can enable the adapter to accept changes in the configuration
without user input. When this mode is enabled (see “Changing the
RAID Parameters” on page 121 for information), the adapter pauses
briefly to permit a user to override the default action; then the
adapter makes the necessary changes. Unattended mode also clears
any locked stripes and any blocked logical drives. This mode is
useful when the server operates remotely.
The adapter “chooses” an action that is equivalent to pressing one
of the following function key:
F5:
The server continues the startup operation after identifying the
drive that is defunct. For example, an HSP drive failed to respond
during POST. Startup continues without the HSP drive; its drive
state will display as DHS.
F6:
When a drive has been removed from the server, for example,
for maintenance or security, and was returned, but in a different
bay, the adapter adjusts the configuration to the drive's new
location.
Chapter 3. Configuring the Disk Array
123