A file system that can be resized online is recommended in that it allows the system to adjust its storage on-the-fly without interrupting applications. Changing the size of the LV does not necessarily change the size of a file system on it it merely changes the size of its containing space. Some volume managers allow the re-sizing of LVs in either direction while online. This allows LVs to grow without having to move already-allocated LEs. The concatenated LEs do not have to be contiguous. Striped LVs allocate each successive LE from a different PV depending on the size of the LE, this can improve performance on large sequential reads by bringing to bear the combined read-throughput of multiple PVs.Īdministrators can grow LVs (by concatenating more LEs) or shrink them (by returning LEs to the pool). Systems can use LVs as raw block devices just like disk partitions: creating mountable file systems on them, or using them as swap storage. The pooled LEs can then be concatenated together into virtual disk partitions called logical volumes or LVs. The system pools LEs into a volume group (VG). PVGs are usually laid out so that they reside on different disks or data buses for maximum redundancy. These PEs are drawn from a physical volume group (PVG), a set of same-sized PVs which act similarly to hard disks in a RAID1 array. With mirroring, multiple PEs map to each LE. Normally, PEs simply map one-to-one to logical extents (LEs). Some volume managers (such as that in HP-UX and Linux) have PEs of a uniform size others (such as that in Veritas) have variably-sized PEs that can be split and merged at will. Volume management treats each PV as being composed of a sequence of chunks called physical extents (PEs). They start with physical volumes (PVs), which can be either hard disks, hard disk partitions, or Logical Unit Numbers (LUNs) of an external storage device. Most volume-manager implementations share the same basic design.
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