LVMify the disk - Revision history

Adj at 18:10, 4 January 2011

2011-01-04T18:10:51Z

Adj: /* Move stuff to LVM */

2011-01-04T17:18:31Z

Move stuff to LVM

← Older revision		Revision as of 17:18, 4 January 2011
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	/dev/vg00/var /var ext3 defaults 0 0		/dev/vg00/var /var ext3 defaults 0 0
	Also, comment out the line that lists /tmp on a tmpfs (RAM-backed) filesystem.		Also, comment out the line that lists /tmp on a tmpfs (RAM-backed) filesystem.
			== see if it worked ==
			Now is time to reboot, log in again, and see if it's all working as expected. After rebooting, /home, /tmp, /usr, and /var should be mounted from LVM logical volumes. You'll see them listed as <code>/dev/mapper/vg00-{home,tmp,usr,var}</code> in the output of <code>mount</code> or <code>df</code>. If something isn't working correctly, removing the LVM entries from <code>/etc/fstab</code> and rebooting again will leave you with just the root filesystem, still intact, on <code>/dev/sda1</code>.

Adj at 22:29, 3 January 2011

2011-01-03T22:29:33Z

@@ Line 172: / Line 172: @@
  root@canopus:/# find . -xdev -depth -print0 | cpio -pdmv0a /altroot
  [...]
- root@canopus:~#
+ root@canopus:~# umount /altroot
-With this done, you can use /dev/sda2 as your root filesystem by changing the "root=/dev/sda1" kernel command line prarameter (set in the bootloader to "root=/dev/sda2".
+With this done, you can use /dev/sda2 as your root filesystem by changing the "root=/dev/sda1" kernel command line prarameter (set in the bootloader) to "root=/dev/sda2".

Adj at 21:49, 3 January 2011

2011-01-03T21:49:34Z

← Older revision		Revision as of 21:49, 3 January 2011
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	/dev/dm-0 partition 524280 0 -1		/dev/dm-0 partition 524280 0 -1
	root@canopus:~#		root@canopus:~#

			/dev/sda2 is no longer being used for swap space and we can now put a backup root filesystem there.
			= Make a backup root filesystem =
			Now that we've stopped using /dev/sda2 for swap, let's put our backup root FS there. We'll format it with mkfs.ext2, mount it someplace convenient, and copy our files over.
			== create an ext2 filesystem on /dev/sda2 ==
			root@canopus:~# mkfs.ext2 -T ext2 /dev/sda2
			mke2fs 1.41.12 (17-May-2010)
			Filesystem label=
			OS type: Linux
			Block size=4096 (log=2)
			Fragment size=4096 (log=2)
			Stride=0 blocks, Stripe width=0 blocks
			32768 inodes, 131072 blocks
			6553 blocks (5.00%) reserved for the super user
			First data block=0
			Maximum filesystem blocks=134217728
			4 block groups
			32768 blocks per group, 32768 fragments per group
			8192 inodes per group
			Superblock backups stored on blocks:
			32768, 98304

			Writing inode tables: done
			Writing superblocks and filesystem accounting information: done

			This filesystem will be automatically checked every 24 mounts or
			180 days, whichever comes first. Use tune2fs -c or -i to override.
			root@canopus:~#
			== populate the backup ==
			I like to use <code>/altroot</code> for this purpose. My normal idiom for creating the directory underlying a mount point is to give it 000 (or d---------) permissions. Makes it obvious to me that something should be mounted there:
			root@canopus:~# mkdir -m 0 /altroot
			root@canopus:~# mount /dev/sda2 /altroot
			root@canopus:~# cd /
			root@canopus:/# find . -xdev -depth -print0 \| cpio -pdmv0a /altroot
			[...]
			root@canopus:~#
			With this done, you can use /dev/sda2 as your root filesystem by changing the "root=/dev/sda1" kernel command line prarameter (set in the bootloader to "root=/dev/sda2".

Adj: /* Reconfiguring swap location */

2011-01-03T21:28:41Z

Reconfiguring swap location

← Older revision		Revision as of 21:28, 3 January 2011
Line 130:		Line 130:
	tmpfs /tmp tmpfs defaults 0 0		tmpfs /tmp tmpfs defaults 0 0
	/dev/vg00/swap none swap sw 0 0		/dev/vg00/swap none swap sw 0 0
			root@canopus:~#

			Just to be sure /dev/sda2 is not being used any more as swap space, have a look at /proc/swaps:
			root@canopus:~# cat /proc/swaps
			Filename Type Size Used Priority
			/dev/dm-0 partition 524280 0 -1
	root@canopus:~#		root@canopus:~#

Adj: /* Making our first logical volume: /dev/vg00/swap */

2011-01-03T21:26:21Z

Making our first logical volume: /dev/vg00/swap

← Older revision		Revision as of 21:26, 3 January 2011
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	Logical volume "swap" created		Logical volume "swap" created
	root@canopus:~#		root@canopus:~#
			== Reconfiguring swap location ==
	After this logical volume has been created, we'll put the swap space signature on it using <code>mkswap</code>, activate it with <code>swapon</code>, deactivate the old one (<code>swapoff</code>), and update /etc/fstab to save the changes across a reboot:		After this logical volume has been created, we'll put the swap space signature on it using <code>mkswap</code>, activate it with <code>swapon</code>, deactivate the old one (<code>swapoff</code>), and update /etc/fstab to save the changes across a reboot:
	root@canopus:~# mkswap /dev/vg00/swap		root@canopus:~# mkswap /dev/vg00/swap

Adj: Created page with "= LVM? What's this all about, anyway? = LVM Linux's Logical Volume Manager. Wikipedia [http://en.wikipedia.org/wiki/Logical_Volume_Manager_%28Linux%29 describes the Linux LVM h…"

2011-01-03T21:25:15Z

Created page with "= LVM? What's this all about, anyway? = LVM Linux's Logical Volume Manager. Wikipedia [http://en.wikipedia.org/wiki/Logical_Volume_Manager_%28Linux%29 describes the Linux LVM h…"

New page

= LVM? What's this all about, anyway? =
LVM Linux's Logical Volume Manager. Wikipedia [http://en.wikipedia.org/wiki/Logical_Volume_Manager_%28Linux%29 describes the Linux LVM here.] Basically, it allows you to take a pool of one or more hard drives and create one or more virtual hard drives out of piecs of the real drives. These can then be resized at run-time, allowing the admin to grow (or sometimes) shrink filesystems while the machine is up and running. This page covers the moving of a hard-partitioned Seagate DockStar running Debian to an LVM-based setup.

= Before LVM-ification =
Got a backup? You could bork your machine pretty hard if something bad happens. You've been warned.

Here's how the DockStar's USB flash drive looks now with regard to filesystem free space and partitioning:
root@canopus:~# fdisk -l -u /dev/sda

Disk /dev/sda: 4000 MB, 4000317440 bytes
64 heads, 32 sectors/track, 3815 cylinders, total 7813120 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x9a198ead

Device Boot Start End Blocks Id System
/dev/sda1 * 2048 1050623 524288 83 Linux
/dev/sda2 1050624 2099199 524288 83 Linux
/dev/sda3 2099200 7813119 2856960 8e Linux LVM
root@canopus:~# df
Filesystem 1K-blocks Used Available Use% Mounted on
rootfs 516040 311876 177952 64% /
none 60492 36 60456 1% /dev
/dev/sda1 516040 311876 177952 64% /
tmpfs 62864 0 62864 0% /lib/init/rw
tmpfs 62864 0 62864 0% /dev/shm
tmpfs 62864 0 62864 0% /tmp
root@canopus:~# cat /etc/fstab
# /etc/fstab: static file system information.
#
# <file system> <mount point> <type> <options> <dump> <pass>
/dev/root / ext2 noatime,errors=remount-ro 0 1
/dev/sda2 none swap sw 0 0
tmpfs /tmp tmpfs defaults 0 0
root@canopus:~#
= The current situation =
As you can probably tell, the only filesystem is on /dev/sda1 and /dev/sda2 is used for swap space. /dev/sda3 is not used for anything at this point.
= The desired end state =
I'd like to end up with /dev/sda1 used purely for system configuration and needed-for-boot files. Swap space, /var, /home, /tmp, and /usr will all live in LVM managed block devices. /dev/sda2 will be converted from swap space to a working backup copy of the current root filesystem and used for repairing the real system should the sysadmin suffer a severe bout of brain-damage and break the thing really bad.

Based on lots of use of <code>du</code>, I believe 512Mbytes for swap, 64Mbytes for /home, 128Mbytes for /tmp, 192Mbytes for /usr, and 192Mbytes for /var will be a good target configuration.
= Creating an LVM physical volume =
Some data structures need to be placed on a physical device that LVM uses. This is done with the <code>pvcreate</code> program. <code>/dev/sda3</code> is where we'll put the LVM managed logical volumes, so <code>pvcreate</code> is invoked so (in test mode first, to be sure our command line is sane):
root@canopus:~# pvcreate --test --verbose --metadatatype 2 --pvmetadatacopies 2 --zero y /dev/sda3
Test mode: Metadata will NOT be updated.
Set up physical volume for "/dev/sda3" with 5713920 available sectors
Zeroing start of device /dev/sda3
Physical volume "/dev/sda3" successfully created
Test mode: Wiping internal cache
Wiping internal VG cache
root@canopus:~# pvcreate --verbose --metadatatype 2 --pvmetadatacopies 2 --zero y /dev/sda3
Set up physical volume for "/dev/sda3" with 5713920 available sectors
Zeroing start of device /dev/sda3
Physical volume "/dev/sda3" successfully created
root@canopus:~#
= Creating a volume group =
Now that there is a physical volume, we can create a volume group. We're specifying that this volume group will not be clustered, is an LVM2 volume group (the tools support the older LVM1 format, too), a physical extent size of 64Mibibytes (this is the size of the pieces that go into any given logical volume. Since the backing store for this volume group is about 3Gibibytes in size, a 64Mibibyte gives us 43 pieces of that to play with), a volume group name of vg00, and that /dev/sda3 is our physical backing device. Again, test mode is used to ensure sanity of command line before really creating the volume group.
root@canopus:~# vgcreate --test --verbose --clustered n --metadatatype 2 --physicalextentsize 64M vg00 /dev/sda3
Test mode: Metadata will NOT be updated.
Wiping cache of LVM-capable devices
Wiping cache of LVM-capable devices
Adding physical volume '/dev/sda3' to volume group 'vg00'
Test mode: Skipping archiving of volume group.
Test mode: Skipping volume group backup.
Volume group "vg00" successfully created
Test mode: Wiping internal cache
Wiping internal VG cache
root@canopus:~# vgcreate --verbose --clustered n --metadatatype 2 --physicalextentsize 64M vg00 /dev/sda3
Wiping cache of LVM-capable devices
Wiping cache of LVM-capable devices
Adding physical volume '/dev/sda3' to volume group 'vg00'
Creating directory "/etc/lvm/archive"
Archiving volume group "vg00" metadata (seqno 0).
Creating directory "/etc/lvm/backup"
Creating volume group backup "/etc/lvm/backup/vg00" (seqno 1).
Volume group "vg00" successfully created
root@canopus:~#
= Making /dev/sda2 available =
/dev/sda2 is currently used as swap space. It's the same size as /dev/sda1. I want to deactivate the swap space here and make a copy of the root filesystem. First, though, there should be a different swap space make available.
== Making our first logical volume: /dev/vg00/swap ==
Creating a logical volume is done with the <code>lvcreate</code> command. You want to decide a few things before creating one: how big should it be? What name should it have? Which volume group does it belong to?

Here's what I did to make /dev/vg00/swap:
root@canopus:~# lvcreate --test --verbose --size 512M --name swap --zero y vg00
Test mode: Metadata will NOT be updated.
Setting logging type to disk
Finding volume group "vg00"
Test mode: Skipping archiving of volume group.
Creating logical volume swap
Test mode: Skipping volume group backup.
Found volume group "vg00"
Aborting. Failed to activate new LV to wipe the start of it.
Found volume group "vg00"
Unable to deactivate failed new LV. Manual intervention required.
Test mode: Wiping internal cache
Wiping internal VG cache
root@canopus:~# lvcreate --verbose --size 512M --name swap --zero y vg00
Setting logging type to disk
Finding volume group "vg00"
Archiving volume group "vg00" metadata (seqno 5).
Creating logical volume swap
Creating volume group backup "/etc/lvm/backup/vg00" (seqno 6).
Found volume group "vg00"
Creating vg00-swap
Loading vg00-swap table (254:0)
Resuming vg00-swap (254:0)
Clearing start of logical volume "swap"
Creating volume group backup "/etc/lvm/backup/vg00" (seqno 6).
Logical volume "swap" created
root@canopus:~#
After this logical volume has been created, we'll put the swap space signature on it using <code>mkswap</code>, activate it with <code>swapon</code>, deactivate the old one (<code>swapoff</code>), and update /etc/fstab to save the changes across a reboot:
root@canopus:~# mkswap /dev/vg00/swap
mkswap: /dev/vg00/swap: warning: don't erase bootbits sectors
on whole disk. Use -f to force.
Setting up swapspace version 1, size = 524284 KiB
no label, UUID=76b70850-c3ab-4512-b55b-0545f2690130
root@canopus:~# swapon /dev/vg00/swap
root@canopus:~# swapoff /dev/sda2
root@canopus:~# sed -e'/^\/dev\/sda2/s/^/# /' /etc/fstab > /tmp/fstab
root@canopus:~# echo '/dev/vg00/swap none swap sw 0 0' >> /tmp/fstab
root@canopus:~# install -o root -g root -m 644 /tmp/fstab /etc/fstab
root@canopus:~# cat /etc/fstab
# /etc/fstab: static file system information.
#
# <file system> <mount point> <type> <options> <dump> <pass>
/dev/root / ext2 noatime,errors=remount-ro 0 1
# /dev/sda2 none swap sw 0 0
tmpfs /tmp tmpfs defaults 0 0
/dev/vg00/swap none swap sw 0 0
root@canopus:~#