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 at 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 at 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 at 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.