Last time, so long ago it isn't even funny, I walked through the process of migrating data from an old hard drive to a new, bigger hard drive, with the help of some LVM2 magic. In that case the partitions---more accurately logical volumes (LVs)---stayed intact, floating on top of the LVM2 mapping layer as physical volumes (PVs) were shuffled around beneath them. The ext3 file systems remained the same size they had been before the move in spite of the extra available disk space.
After making sure that things are backed up, and prior to starting this exercise, we will acquaint ourselves with the lay of the land. First, we see what file systems are currently mounted, limiting the output to only those of ext3 type with
# mount -t ext3 /dev/mapper/vg_elaine-lv_root on / type ext3 (rw,errors=remount-ro) /dev/md1 on /boot type ext3 (rw) /dev/mapper/vg_elaine-lv_home on /home type ext3 (rw) /dev/mapper/vg_elaine-lv_tmp on /tmp type ext3 (rw) /dev/mapper/vg_elaine-lv_usr on /usr type ext3 (rw) /dev/mapper/vg_elaine-lv_var on /var type ext3 (rw)
Next, to demonstrate why an upgrade is desirable, we output the amount of disk free space (
df), in byte-oriented form (
-h as in "for humans"), of only ext3 file systems (
# df -h -t ext3 Filesystem Size Used Avail Use% Mounted on /dev/mapper/vg_elaine-lv_root 496M 137M 334M 30% / /dev/md1 130M 13M 110M 11% /boot /dev/mapper/vg_elaine-lv_home 35G 20G 14G 59% /home /dev/mapper/vg_elaine-lv_tmp 496M 19M 452M 4% /tmp /dev/mapper/vg_elaine-lv_usr 5.3G 543M 4.5G 11% /usr /dev/mapper/vg_elaine-lv_var 1008M 153M 805M 16% /var
Note that the
/home system is nearly two thirds full, and in absolute terms is unsuitable as a resource for scheduled backups of large sub-trees, which is what it is now needed for.
pvscan command shows that the RAID set used as the foundation of this volume group (VG) has quit a bit of room that has not yet been allocated to any LVs.
# pvscan PV /dev/md2 VG vg_elaine lvm2 [232.75 GB / 189.40 GB free] Total: 1 [232.75 GB] / in use: 1 [232.75 GB] / in no VG: 0 [0 ] # lvscan ACTIVE '/dev/vg_elaine/lv_root' [512.00 MB] inherit ACTIVE '/dev/vg_elaine/lv_swap' [1.00 GB] inherit ACTIVE '/dev/vg_elaine/lv_tmp' [512.00 MB] inherit ACTIVE '/dev/vg_elaine/lv_var' [1.00 GB] inherit ACTIVE '/dev/vg_elaine/lv_usr' [5.35 GB] inherit ACTIVE '/dev/vg_elaine/lv_home' [35.00 GB] inherit
The plan is to take 150 GB of the available 190-ish GB and use it to make
lv_home bigger. I will leave the rest alone for now in anticipation of the day when
lv_root or perhaps
lv_usr needs a little boost.
Three of the tools in the LVM2 suite seem to be interconnected somehow. They are
lvextend. From what I can tell, the latter pair are just the two operations that are possible with the first, and so I will use
lvextend so that there is marginally less chance of doing damage.
The easy part
Making the LV bigger is very quick, and very easy.
# lvextend -L +150G /dev/vg_elaine/lv_home Extending logical volume lv_home to 185.00 GB Logical volume lv_home successfully resized
To verify, we can check like this.
# lvdisplay /dev/vg_elaine/lv_home --- Logical volume --- LV Name /dev/vg_elaine/lv_home VG Name vg_elaine LV UUID OeNy9W-6MRf-BIGj-GJHE-gjRZ-Efps-oLch1U LV Write Access read/write LV Status available # open 1 LV Size 185.00 GB (sure enough, the volume has grown) Current LE 47360 Segments 1 Allocation inherit Read ahead sectors 0 Block device 253:5
But the file system itself is still relatively small.
# df -h /home Filesystem Size Used Avail Use% Mounted on /dev/mapper/vg_elaine-lv_home 35G 20G 14G 59% /home
The hard part
Now it's time to make the file system bigger. While there is some information around that suggests that online resizing (i.e. resizing without first unmounting) is possible with ext3 under the 2.6 kernel, I would consider that brash at best.
The command we're about to use is
resize2fs. The manpage claims that if the size parameter is omitted, it will grow the file system to completely fill the underlying device. Therefore the only parameters will be the device and the
-p option to show progress.
resize2fs requires that you perform a consistency check on the file system so that it is marked "clean" prior to resizing it. This is not specified in the manpage, but if you try skipping this step, you'll be reminded.
The whole process is supposed to happen in four, closely spaced operations: 1) unmount the file system; check it; 3) resize it; and 4) remount it. If #3 breaks, I don't know whether there will be any alternative to wiping the device, creating a new file system from scratch, and restoring the
/home subtree from the backup, but I am fully prepared to do that if this goose flies south.
In order to unmount
/home, I will first have to release it by performing an NFS unexport as follows.
# exportfs -u ClientIP:/home
# umount /home # e2fsck -f /dev/mapper/vg_elaine-lv_home e2fsck 1.40-WIP (14-Nov-2006) Pass 1: Checking inodes, blocks, and sizes Pass 2: Checking directory structure Pass 3: Checking directory connectivity Pass 4: Checking reference counts Pass 5: Checking group summary information home: 3166/4587520 files (2.7% non-contiguous), 5131561/9175040 blocks # resize2fs -p /dev/mapper/vg_elaine-lv_home resize2fs 1.40-WIP (14-Nov-2006) Resizing the filesystem on /dev/mapper/vg_elaine-lv_home to 48496640 (4k) blocks. Begin pass 1 (max = 1200) Extending the inode table XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX The filesystem on /dev/mapper/vg_elaine-lv_home is now 48496640 blocks long. # mount /home
Everything looks good. Let's see what
# df -h /home Filesystem Size Used Avail Use% Mounted on /dev/mapper/vg_elaine-lv_home 183G 20G 154G 12% /home
No twitching, or hiccups. No smell of smoke. I think it's safe to unclench.
The tool versions used above are as follows.
# cat /etc/debian_version 4.0 # lvm version LVM version: 2.02.07 (2006-07-17) Library version: 1.02.08 (2006-07-17) Driver version: 4.7.0 # uname -r 2.6.18-6-k7 # df --version df (GNU coreutils) 5.97 [snip] # resize2fs resize2fs 1.40-WIP (14-Nov-2006) [snip]