On current storage systems, individual disks are only visible to a certain extent. BS2000 sees “logical volumes” which are assigned to the LUNs (Logical Unit Numbers). The assignment of LUNs to physical disks is largely hidden from BS2000. The storage systems ensure efficient operation by means of RAID levels.
“Large” logical volumes can also be used. These are volumes which are more than 32 GB in size, see the manual “Files and Volumes greater than 32 GB” [3 (Related publications)].
Logical volumes and physical disks
From the BS2000 viewpoint logical volumes are independent units on which I/O operations can be initiated in parallel. When the current high-capacity disks are used, multiple logical volumes are normally located on a disk drive.
When I/O operations on logical volumes located on the same disk drive are initiated in parallel, the hardware service time of magnetic disks is inevitably extended. Whether the extension of the hardware service time leads to an appreciable performance loss depends on the cache hit rate and the utilization of the disk drive – possibly also by users outside BS2000. SSDs are significantly better in handling parallel IOs. A significant extension of IO times is only expected when the overall load exceeds a certain limit.
Nowadays, storage space is usually provided via thin provisioning. The distribution of the logical volumes for BS2000 to the physical disks within a configured thin provisioning pool is managed by the storage system.
Requirements for configuring storage systems
From the BS2000 viewpoint, the disk peripherals are subject to different requirements:
- capacity
- throughput
- reaction times
- parallel use
Although the need for manual optimization is reduced when using thin provisioning and the algorithms of the storage systems ensure an optimal distribution of logical volumes onto physicasl disks, there are still performance relevant factors to be considered when selecting and configuring a certain thin provisioning pool to select a suitable
- disk type
- and RAID level
Data format
It is recommended to use NK2 data format. Compared to K data format, in which the key information is also included, NK data format makes better use of the disk capacity and the cache memory, thus achieving shorter hardware service times.
Use of SHC-OSD
You can ascertain the following with SHC-OSD:
the RAID group in which a BS2000 volume resides
which other volumes reside in the same RAID group
The drive workload on ETERNUS DX/AF cannot be determined using BS2000 resources and can therefore not be measured using openSM2. It consists of the sum of the I/O loads of the relevant logical volumes.