Virtual provisioning requires specially configured device types in the storage system, so-called thin devices and data devices.
Thin devices
The server sees a thin device in its configured size. Internally it must always be assigned to a thin pool in which the resources are contained.
When an area of the thin device is written to, the storage system assigns the thin device a minimum amount of physical storage from the thin pool.
When a read operation takes place on a thin device, the data is read from the data device in the thin pool to which the thin device is assigned. The thin pools are assigned further data devices to satisfy enhanced capacity requirements for writes of the thin devices.
When more storage is required for existing or future thin devices, existing thin pools can also be extended dynamically by additional data devices.
New thin devices which can be accessed and used by the server are configured dynamically in the storage system and assigned to the thin pools. They must be generated like normal units when hardware generation of BS2000 takes place with IOGEN (/390 servers) or in X2000 (x86 servers).
The /SHOW-SYMMETRIX-DEVICE-CONFIG RAID=*TDEV command selects thin devices. These are labeled with T in the RAID column.
The /SHOW-SYMMETRIX-DEVICE-CONFIG INFORMATION=*THIN-DEVICES command displays the specific properties of a thin device with the assignment to a thin pool and the specific capacity values.
See the examples on "SHOW-SYMMETRIX-DEVICE-CONFIG Displays the device configuration (Symmetrix/VMAX3)".
Monitoring the thin devices
SHC-OSD monitors the occupancy levels of the thin devices.
Message NDE0074 (which you can answer) on the console shows when a particular limit value for the occupancy level of a thin device has been exceeded. The THIN-DEV-SAT operand in the /MODIFY-SHC-PROCESSING command or the THIN-DEVICE-SATURATION parameter in the SHC-OSD parameter file determines the limit value (default value 80%). The current value can be inquired with /SHOW-SHC-PROCESSING.
When the limit value is reached, administrative intervention enables capacity to be provided again.
Data devices
Data devices are internal devices which are configured in the storage system and provide storage space for storing the contents of the thin devices. Data devices cannot be accessed by the server.
A sufficient number of adequately sized data devices must be configured and activated.
The /SHOW-SYMMETRIX-DEVICE-CONFIG TYPE=*DATA-DEVcommand selects data devices. These are labeled with DATA-DEV in the TYPE column.
The /SHOW-SYMMETRIX-DEVICE-CONFIG INFORMATION=*DATA-DEVICES command displays the specific properties of a data device with the assignment to a thin pool and the specific capacity values. See the examples on "SHOW-SYMMETRIX-DEVICE-CONFIG Displays the device configuration (Symmetrix/VMAX3)".
Thin pools
Data devices are managed in the storage system in so-called thin pools. Each thin pool is available to the user in its entirety for his/her thin devices.
CAUTION!
When a thin pool is full (overflow), no more storage space can be provided for the assigned thin devices for writes. The applications which are using it encounter an error (remount message). The functions of SHC-OSD for monitoring the thin pools should thus be used.
In Symmetrix, setting up multiple thin pools permits partitioning, for example by having the thin devices of various applications which operate with different pubsets assigned to different thin pools.
The /SHOW-SYMMETRIX-CONFIGURATION INFORMATION=*THIN-POOLS command displays information on the thin pools, including their current occupancy levels. See the example on "SHOW-SYMMETRIX-CONFIGURATION Displays the configuration (Symmetrix/VMAX3)".
Monitoring the thin pools
SHC-OSD offers monitoring of the occupancy levels of the monitored thin pools for the storage system. See also the THIN-POOL-MONITORING parameter in the SHC-OSD parameter file (see the section "Configuration of SHC-OSD").
Messages NDE0070 and NDE0071 (which you can answer) on the console show when a particular limit value for the occupancy level of a thin pool has been exceeded. The THIN-POOL-SAT operand in the /MODIFY-SHC-PROCESSING command or the THIN-POOL-SATURATION parameter in the SHC-OSD parameter file determines the limit value (default value 80%). The current value can be inquired with /SHOW-SHC-PROCESSING.
When the limit value is reached, administrative intervention enables further capacity to be provided in the thin pool; the thin pool in the storage system can be extended by further data devices. When sufficient space is once more available in the thin pool, this is indicated by messages NDE0075/NDE0076 on the console. Messages NDE0070/NDE0071 are then answered automatically.