On 06/25/2015 01:20 PM, Chris Adams wrote:
...It's basically a way to assemble one arbitrary set of block devices
and then divide them into another arbitrary set of block devices, but
now separate from the underlying physical structure.
Regular partitions have various limitations (one big one on Linux
being that modifying the partition table of a disk with in-use
partitions is a PITA and most often requires a reboot), and LVM
abstracts away some of them. ....
I'll give an example. I have a backup server, and for various reasons
(hardlinks primarily) all the data needs to be in a single filesystem.
However, this is running on an older VMware ESX server, and those have a
2TB LUN size limit. So, even though my EMC Clariion arrays can deal
with 10TB LUNs without issue, the VMware ESX and all of its guests
cannot. So, I have a lot of RDMs for the guests. The backup server's
LVM looks like this:
[root@backup-rdc ~]# pvscan
PV /dev/sdd1 VG vg_opt lvm2 [1.95 TB / 0 free]
PV /dev/sde1 VG vg_opt lvm2 [1.95 TB / 0 free]
PV /dev/sdf1 VG vg_opt lvm2 [1.95 TB / 0 free]
PV /dev/sda2 VG VolGroup00 lvm2 [39.88 GB / 0 free]
PV /dev/sdg1 VG bak-rdc lvm2 [1.95 TB / 0 free]
PV /dev/sdh1 VG bak-rdc lvm2 [1.95 TB / 0 free]
PV /dev/sdi1 VG bak-rdc lvm2 [1.95 TB / 0 free]
PV /dev/sdj1 VG bak-rdc lvm2 [1.95 TB / 0 free]
PV /dev/sdk1 VG bak-rdc lvm2 [1.47 TB / 0 free]
PV /dev/sdl1 VG bak-rdc lvm2 [1.47 TB / 0 free]
PV /dev/sdm1 VG bak-rdc lvm2 [1.95 TB / 0 free]
PV /dev/sdn1 VG bak-rdc lvm2 [1.95 TB / 0 free]
PV /dev/sdo1 VG bak-rdc lvm2 [1.95 TB / 0 free]
PV /dev/sdp1 VG bak-rdc lvm2 [1.95 TB / 0 free]
PV /dev/sdq1 VG bak-rdc lvm2 [1.95 TB / 0 free]
PV /dev/sdr1 VG bak-rdc lvm2 [1.95 TB / 0 free]
PV /dev/sdb1 VG bak-rdc lvm2 [1.95 TB / 0 free]
PV /dev/sdc1 VG bak-rdc lvm2 [1.95 TB / 0 free]
Total: 18 [32.27 TB] / in use: 18 [32.27 TB] / in no VG: 0 [0 ]
[root@backup-rdc ~]# lvscan
ACTIVE '/dev/vg_opt/lv_backups' [5.86 TB] inherit
ACTIVE '/dev/VolGroup00/LogVol00' [37.91 GB] inherit
ACTIVE '/dev/VolGroup00/LogVol01' [1.97 GB] inherit
ACTIVE '/dev/bak-rdc/cx3-80' [26.37 TB] inherit
[root@backup-rdc ~]#
It's just beautiful the way I can take another 1.95 TB LUN, add it to
the volume group, expand the logical volume, and then expand the
underlying filesystem (XFS) and just dynamically add storage. Being on
an EMC Clariion foundation, I don't have to worry about the RAID,
either, as the RAID6 and hotsparing is done by the array. SAN and LVM
were made for each other. And, if and when I either migrate the guest
over to physical hardware on the same SAN or migrate to some other
virtualization, I can use LVM's tools to migrate from all those 1.95 and
1.47 TB LUNs over to a few larger LUNs and blow away the smaller LUNs
while the system is online. And the EMC Clariion FLARE OE software
allows me great flexibility in moving LUNs around in the array for
performance and other reasons.
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