Redirect Data From Unreliable Blocks (Hot Fix) - Novell NETWARE 6-DOCUMENTATION Manual

Redirect Data from Unreliable Blocks (Hot Fix)

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Novell Storage Services Administration Guide
As your file system constantly reads and writes data to disk, some disk storage
blocks lose their ability to reliably store data. NSS uses Hot Fix to prevent data
from being written to unreliable blocks.
Hot Fix redirects the original block of data (still in memory) to the Hot Fix
TM
Redirection Area of the partition where the data can be stored correctly. To
redirect a block of data, the operating system records the address of the
defective block. Then the server no longer attempts to store data in that block.
If you do not enable Hot Fix when you create a partition, then no Hot Fix
object is created and no data redirection can occur. You need to set up Hot Fix
when you create the partition. To add Hot Fix later, you must delete the
volumes from the partition, add Hot Fix, then restore the volumes from a
backup.
The Hot Fix feature is combined with partition mirroring. When you select
Hot Fix, you also enable mirroring for that partition.
Hot Fix redirection can occur during a write request, a read request, or a read-
after-write verification. The following are conditions of data redirection:
Write redirection occurs when the disk reports an error during a write
request. The system marks the block as bad and redirects the data to a
different block.
Read redirection occurs when a disk error happens during a read request.
If the disk is mirrored, the system retrieves the data from the mirrored
disk and redirects the data on the primary disk. If the disk is not mirrored,
the data is lost, and the block is marked as unusable.
Read-after-write-verify redirection occurs after data is written to disk.
The data on disk is then read and compared to that in memory. If the two
don't match, the system marks the block as bad and redirects the data to
a different block.
By default, 2 percent of a disk's space is set aside as the Hot Fix Redirection
Area. You can increase or decrease this amount.
If Hot Fix is enabled, then it is always active unless the disk fails or the
redirection area is full. You can view Hot Fix activity in MONITOR by
selecting Storage Devices and then a Hot Fix partition. For information on
using MONITOR, see MONITOR in the Utilities Reference.