Logical Volumes; Allocation, Deletion, And Modification Of Volumes - IBM DS8880 Series Introduction And Planning Manual

v This feature requires changes in the I/O stack to take advantage of all the
v T10 DIF volumes can be used by any type of Open host with the exception of
v T10 DIF volumes can accept SCSI I/O of either T10 DIF or standard type, but if

Logical volumes

A logical volume is the storage medium that is associated with a logical disk. It
typically resides on two or more hard disk drives.
For the storage unit, the logical volumes are defined at logical configuration time.
For count-key-data (CKD) servers, the logical volume size is defined by the device
emulation mode and model. For fixed block (FB) hosts, you can define each FB
volume (LUN) with a minimum size of a single block (512 bytes) to a maximum
size of 2
A logical device that has nonremovable media has one and only one associated
logical volume. A logical volume is composed of one or more extents. Each extent
is associated with a contiguous range of addressable data units on the logical
volume.

Allocation, deletion, and modification of volumes

Extent allocation methods (namely, rotate volumes and pool striping) determine
the means by which actions are completed on storage system volumes.
All extents of the ranks assigned to an extent pool are independently available for
allocation to logical volumes. The extents for a LUN or volume are logically
ordered, but they do not have to come from one rank and the extents do not have
to be contiguous on a rank. This construction method of using fixed extents to
form a logical volume in the storage system allows flexibility in the management
of the logical volumes. You can delete volumes, resize volumes, and reuse the
extents of those volumes to create other volumes, different sizes. One logical
volume can be deleted without affecting the other logical volumes defined on the
same extent pool.
Because the extents are cleaned after you delete a volume, it can take some time
until these extents are available for reallocation. The reformatting of the extents is a
background process.
There are two extent allocation methods used by the storage system: rotate
volumes and storage pool striping (rotate extents).
Storage pool striping: extent rotation
The default storage allocation method is storage pool striping. The extents of a
volume can be striped across several ranks. The storage system keeps a sequence
of ranks. The first rank in the list is randomly picked at each power on of the
storage subsystem. The storage system tracks the rank in which the last allocation
started. The allocation of a first extent for the next volume starts from the next
rank in that sequence. The next extent for that volume is taken from the next rank
in sequence, and so on. The system rotates the extents across the ranks.
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DS8880 Introduction and Planning Guide
capabilities the protection offers.
iSeries, but active protection is supported only for Linux on IBM Z or AIX on
™
IBM Power Systems . The protection can only be active if the host server has
T10 DIF enabled.
the FB volume type is standard, then only standard SCSI I/O is accepted.
32
blocks or 16 TB.