LVM Mirroring - Tried It ?

[Carl Farnsworth_1]

Has anyone actually tested performance of MirrorDisk/UX by pulling
hot-pluggable mirrors and observing system performance? I spent some time
trying it and have two questions.

1. When a mirrored drive is pulled, the system continues to READ just fine,
but the first WRITE (ie mkdir) caused a "hang" of approx. 60 seconds, then
continued just fine. Is this unavoidable (what if MWC is turned off? any
difference?), or can it be SAFELY reduced?

2. Doc's say when system reboots, if quorum not met, vg won't be activated -
and yet I have seen it happen in SOME cases - but I have no idea why! Is it
because lvmtab or lvmconf are being updated before shutdown? even though no
specific vgchanges have been made?

Curious about anyone else's direct experience with this.

[Neil Gast_1]

In response to (1): I have tested in the past, and have not seen delays as long
as you're seeing (60 sec). The delays I saw were in the 15 to 30 second range.
You'll probably still see the hang with or without MWC, as it has more to do
with SCSI bus functionality than with LVM functionality. MWC really has nothing
to do with it.
In response to (2): The quorum requirements are different for boot time than
for run time. Boot time quorum specifies that "one-half plus one" of the
mirrored disks must be present is order to activate the VG. This poses an
obvious problem for those using just one mirror: If the mirror is not available
at boot time, quorum rules state that the VG cannot be activated, and the
system is thus unbootable. To get around this possible problem, do the
following for each disk that is a boot disk:
mkboot -a "hpux -lq" /dev/rdsk/c?t?d?
This installs the "hpux -lq" command in the LIF area of the BDRA on the disk.
The default is just "hpux" with no options. The "-lq" option tells the hpux
command to ignore LVM quorum rules. I would highly recommend doing this on all
of your servers.

Enjoy,
MrNeil


Has anyone actually tested performance of MirrorDisk/UX by pulling
hot-pluggable
mirrors and observing system performance? I spent some time
trying it and have
two questions.

1. When a mirrored drive is pulled, the system continues to
READ just fine, but
the first WRITE (ie mkdir) caused a "hang" of approx. 60
seconds, then continued
just fine. Is this unavoidable (what if MWC is turned off? any
difference?), or can it
be SAFELY reduced?

2. Doc's say when system reboots, if quorum not met, vg won't
be activated -
and yet I have seen it happen in SOME cases - but I have no
idea why! Is it
because lvmtab or lvmconf are being updated before shutdown?
even though no
specific vgchanges have been made?

Curious about anyone else's direct experience with this.

[Fisher Ron]

Has anyone tried using the JFS and LVM mirroring? I am getting the following
error message when adding a mirror and cannot find documentation to help solve
this.

lvlnboot: LIF infomration currupt or not present on "/dev/dsk/c0t5d0"

It tells me to use mkboot and I have used it but I still get the errors.