Step 1: Make backups.
I know, most people skip this step, but you're making changes that can result in major data loss if you screw up, and you're taking guidance from a random stranger on the Internet. You are responsible for the safety of your data. I'm not.
Step 2: Shrink the filesystem in
lv_scratch. If it's an ext2/3/4 filesystem, unmount it and use
resize2fs; if it's something else, you'll need to look up documentation on resizing that type of filesystem.
resize2fs /dev/volgrp01/lv_scratch 50G
When it's done (assuming you're using
resize2fs), it'll tell you the new size of the filesystem in bytes. Make a note of that number, because you can use it for a safety check in the next step.
Step 3: Shrink the logical volume using
- If you want to be simple, use
lvreduce --size 50G volgrp01/lv_scratch.
- If you want to be extra cautious about not shrinking the LV to a size smaller than the filesystem it contains, check the physical extent size of your volume group using
vgdisplay volgrp01, and calculate how many physical extents are needed to hold the byte size of your filesystem (using 1MB = 1048576 bytes). Then specify that number using the
--extents option instead of the
Alternatively, you may be able to skip step 1 and instead use
-r option to resize the filesystem automatically. That may be easier, but I don't have personal experience with it to know how reliable it is.
At this point I'd recommend running
fdisk -f on your
/dev/volgrp01/vg_scratch just to make sure it's intact. If you get any errors about "access beyond end of device", it means you shrunk the LV too much and need to
lvextend it before you proceed.
Step 4: Shrink the physical volume using
pvresize --setphysicalvolumesize 88G /dev/sda2
You don't need an extra safety check here since
pvresize will refuse to shrink the physical volume to a size that's too small for your existing logical volumes. But if the sizes of your other LVs aren't exact multiples of 1GB, the 88G might be too small and you may need use a different value.
Step 5: Shrink the
sda2 partition using
fdisk /dev/sda, and at its prompt, run
p to look at your existing partitions. Note the starting sector number of your
sda2 partition. Then delete the
sda2 partition — this doesn't touch the actual data, just removes the record of where it starts and ends — and create a new
sda2 with the same starting sector (this is vital) and a size of 50G. The partition's type code should be
8e, "Linux LVM".
If you want to be extra cautious — and I'd recommend you do, especially if you had to specify a different size to the
pvresize earlier — check the PE size and Total PE of your physical volume using
pvdisplay /dev/sda2 and multiply them together to find the size of the physical volume in bytes (again using 1MB = 1048576 bytes). Then subtract your new
sda2 partition's starting sector number from its ending one, add 1 so that the last sector is counted, and multiply by your disk's sector size (which should be either 512 or 4096 bytes). Make sure the two results match.
Now create your new
sda3 partition, save your changes, and quit
fdisk. If you get a message about needing to reboot for the change to take effect, reboot.