Interactions Between Mirroring And Striping; Increasing Performance Through I/O Channel Separation; Configuring Lvm I/O Timeout Parameters - HP -UX 11i Administrator's Manual

You might need to experiment to determine the optimum stripe size for your particular situation.
To change the stripe size, re-create the logical volume.

Interactions Between Mirroring and Striping

Mirroring a striped logical volume improves the read I/O performance in a same way that it does
for a nonstriped logical volume. Simultaneous read I/O requests targeting a single logical extent
are served by two or three different physical volumes instead of one. A striped and mirrored logical
volume follows a strict allocation policy; that is, the data is always mirrored on different physical
volumes.
The appendix
logical volumes that are both striped and mirrored.

Increasing Performance Through I/O Channel Separation

I/O channel separation
data reside on LVM disks accessed using separate host bus adapters (HBAs) and cables. I/O
channel separation achieves higher availability and better performance by reducing the number
of single points of possible hardware failure. If you mirror data on two separate disks, but through
one card, your system can fail if the card fails.
You can separate I/O channels on a system with multiple HBAs and a single bus, by mirroring
disks across different HBAs. You can further ensure channel separation by establishing a policy
called PVG-strict allocation, which requires logical extents to be mirrored in separate physical
volume groups. Physical volume groups are subgroups of physical volumes within a volume group.
An ASCII file, /etc/lvmpvg, contains all the mapping information for the physical volume group,
but the mapping is not recorded on disk. Physical volume groups have no fixed naming convention;
you can name them PVG0, PVG1, and so on. The /etc/lvmpvg file is created and updated
using the vgcreate, vgextend, and vgreduce commands, but you can edit the file with a text
editor.
I/O channel separation is useful for databases, because it heightens availability (LVM has more
flexibility in reading data on the most accessible logical extent), resulting in better performance.
If you define your physical volume groups to span I/O devices, you ensure against data loss even
if one HBA fails.
When using physical volume groups, consider using a PVG-strict allocation policy for logical
volumes.

Configuring LVM I/O Timeout Parameters

You can configure the following timeout parameters for LVM I/Os.
Logical volume timeout (LV timeout).
This controls how long LVM retries a logical I/O after a recoverable physical I/O error. LV
timeout can be configured for a specific logical volume using lvchange.
Physical volume timeout (PV timeout).
This is the time budget set by LVM for each physical I/O originating from LVM. The mass
storage stack underlying LVM manages completion of the physical I/O subject to this timeout,
resulting in success or failure for the request. PV timeout can be configured for a specific
physical volume using pvchange.
Mass storage stack timeout parameters
There are mass storage stack tunables that affect LVM I/O timeout behavior: path_fail_secs
and transient_secs.
For details on these timeout parameters, refer to Appendix
"Striped and Mirrored Logical Volumes" (page 157)
is an approach to LVM configuration requiring that mirrored copies of
provides information about
"LVM I/O Timeout Parameters" (page
Configuring LVM I/O Timeout Parameters
161).
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