Root Volume

[Noel Miranda_1]

Hi Intellects

Can anyone explain, WHY ROOT VOLUMES SHOULD BE CONTIGUOUS?

Regards
Noel Miranda

[Michael Tully]

Hi Noel,

If a logical volume is to be used as either root, primary swap, dump or /stand the physical extents must be contiguous.This means that the physical extents of the disk must be allocated with no gaps on a single physical volume. One other reason is that BDRA (Boot Data Reserved Area) needs to be contiguous for booting kernels, saving crash dumps etc

Hope this explains things.....

Michael

[Noel Miranda_1]

Michael,

If a logical volume is to be used as either root, primary swap, dump or /stand the physical extents must be contiguous.This means that the physical extents of the disk must be allocated with no gaps on a single physical volume.

>>> Why is this so??

[Ravi_8]

Hi,
the root filesytem contains the kernel and other os files and root is the highest level filesystem. Since it has to be accessed fast without going through file system, hence it is contiguous

[Steve Lewis · Accepted solution]

I THINK the reason is something like this:
LVM is a driver that is part of the kernel. The IPL (initial program loader) does not contain this driver so does not know about logical to physical extent mappings. However it does know about HFS filesystems and logical volume spaces.
Therefore to boot the system off /stand/vmunix it needs to know the exact position on the boot disk that it is going to find the /stand filesystem and load the kernel file you specify, also to know that the filesystem is going to be on contiguous blocks of disk.
Swap needs to be contiguous for performance reasons and for the ability to use it as a DUMP area, simply writing memory pages to contiguous disk space using a simple algorithm when the system panics.
I think a lot of this may be historical.
What I find interesting is that it is still possible to boot HPUX specifying cXtYdZs1lvm or lvmdisk which means that there must be some knowledge of logical volumes in there somewhere.

[U.SivaKumar_2]

hi,
The reason being to reduce the seek time for the disk access to load the processes like kernel /stand/vmunix , swapped processes without any delay.

regards,
U.SivaKumar