LVM questions for FC3

[Rick Stevens]

Mark wrote:
> Hi,
> 
> I have some questions regarding the use of logical volumes with FC3 systems:
> 
> 1. What happens if a LV spans over mutliple hard disks and one of the disks fails while the server is running?
> Can the server still keep on running on the other disks as long as no data from the broken disk is needed? Or does everything just
> crash once one of the disks dies? As an extreme case, lets assume the broken disk does not contain any files or directories that are
> used at all.

Others may know more since the only LV stuff I do is where the PVs
are actually RAID1, RAID5 or RAID10 disk arrays and I can survive the
loss of a drive.

In your example you aren't striping, so the volume should remain
available as long as the volume doesn't extend onto the failed drive.
If you had striped the LV across the drives, then a failed drive will
fail the LV.

> 2. How big is the performance loss? Obviously, an additional layer in the file system hierarchy does mean additional mapping and
> handling, meaning additional processor usage, meaning performance loss. In most cases this probably does not matter, but what if I
> use the server for example as a mysql database server?

There should be no impact as far as performance is concerned since
you're only involving one spindle at a time.  I sure-as-hell wouldn't
trust the volume for long--you're on very thin ice.
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- Rick Stevens, Senior Systems Engineer     rstevens at vitalstream.com -
- VitalStream, Inc.                       http://www.vitalstream.com -
-                                                                    -
-           Vegetarian:  Old Indian word for "lousy hunter"          -
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