----- Original Message ----- | ----- Original Message ----- | | Hi, | | | | I was wondering, why/when it is useful or when should I avoid to | | use | | LVM. | | | | I think the big advantage of LVMing is if you modify (rezising, | | ...) | | disk and filesystem layouts "a lot". | | | | Are there any real pros or cons for following situations regarding | | e.g. | | management and speed? | | The speed at which you can manage your disk environment through the | use of LVM makes most of the tradeoffs worth while. Of course, YMMV | so you're best to test. | | | e.g.: | | | | I do have a server system raid for which the disk layout will not | | change; e.g. /var /usr /home will not change much in size. | | This isn't so much the issue. What if *any* partition requirements | *do* change in the future. LVM can account for that my allowing you | flexibility to make a change should it be required. Standard | partitioning is less flexible in this regard. | | | OR | | | | I do have some file storage shares (iscsi raids) up to some TB each | | on | | one big storage device. | | | | Sometimes (e.g. after a server crash) it is useful to remount the | | storage to a different server. | | Standard caveats apply. If the Volume Groups or the Logical Volumes | are named the same moving them to another system with similar VGs or | LVs can be problematic. Same goes for file system labels, albeit | both are relatively easy to fix in such a scenario. | | | Should I use LVM on the iscsi storage volumes? | | I would find it difficult to find a case where LVM shouldn't be used | because of it's flexibility. I tend to use full disk LVM (no | partitions at all) and file system labels for mounting and the like | (labels match LVs). | | lvcreate -L 20G -n csgrad DATA | mkfs.xfs -L csgrad /dev/DATA/csgrad | | /etc/fstab | ---------- | | LABEL=csgrad /exports/csgrad xfs defaults 0 0 | | | LVM offers other additional flexibility too in that you can migrate | PVs from one device to another online. So if you have one iSCSI | server that is coming off support and you are replacing it with | another, you can use pvmove to move the data from one target to | another.
Oh! One last case in point. Partition Alignment. This is very important to the performance of a disk subsystem. With full disk LVM it's not an issue at all.