I/O Errors; Recoverable Errors - HP -UX 11i Administrator's Manual

A maintenance mode boot differs from a standard boot as follows:
The system is booted in single-user mode.
No volume groups are activated.
Primary swap and dump are not available.
Only the root file system and boot file system are available.
If the root file system is mirrored, only one copy is used. Changes to the root file system are
not propagated to the mirror copies, but those mirror copies are marked stale and will be
synchronized when the system boots normally.
To boot in maintenance mode on a system with a root disk configured with LVM, use the -lm
option to the boot loader. On an HP 9000 server, enter the following command:
ISL> hpux -lm
On an HP Integrity server, enter the following command:
HPUX> boot -lm
CAUTION:
group and do not change to multiuser mode (for example, by specifying /sbin/init 2). Doing
so can corrupt the root file system.
When you have repaired or restored the LVM configuration information, reboot the system using
the following command:
# /sbin/reboot
For more information about LVM maintenance mode boots and troubleshooting problems with LVM
structures, see Disk and File Management Tasks on HP-UX, published by Prentice Hall PTR, 1997.

I/O Errors

When a device driver returns an error to LVM on an I/O request, LVM classifies the error as either
recoverable or nonrecoverable.

Recoverable Errors

When LVM encounters a recoverable (correctable) error, it internally retries the failed operation
assuming that the error will correct itself or that you can take steps to correct it. Examples of
recoverable errors are the following:
Device power failure
A disk that goes missing after the volume group is activated
A loose disk cable (which looks like a missing disk)
In these cases, LVM logs an error message to the console, but it does not return an error to the
application accessing the logical volume.
If you have a current copy of the data on a separate, functioning mirror, then LVM directs the I/O
to a mirror copy, the same as for a nonrecoverable error. Applications accessing the logical volume
do not detect any error. (To preserve data synchronization between its mirrors, LVM retries
recoverable write requests to a problematic disk, even if a current copy exists elsewhere. However,
this process is managed by a daemon internal to LVM and has no impact on user access to the
logical volume.)
However, if the device in question holds the only copy of the data, LVM retries the I/O request
until it succeeds—that is, until the device responds or the system is rebooted. Any application
performing I/O to the logical volume might block, waiting for the device to recover. In this case,
your application or file system might appear to be stalled and might be unresponsive.
When you boot your system in maintenance mode, do not activate the root volume
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