Lun Calculation - IBM DS8800 Introduction And Planning Manual

LUN calculation

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Introduction and Planning Guide
Managed EAM
Once a volume is managed by Easy Tier, the EAM of the volume is changed to
managed EAM, which can result in placement of the extents differing from the
rotate volume and rotate extent rules. The EAM only changes when a volume is
manually migrated to a non-managed pool.
Rotate volumes allocation method
Extents can be allocated sequentially. In this case, all extents are taken from the
same rank until there are enough extents for the requested volume size or the rank
is full, in which case the allocation continues with the next rank in the extent pool.
If more than one volume is created in one operation, the allocation for each
volume starts in another rank. When allocating several volumes, rotate through the
ranks. You might want to consider this allocation method when you prefer to
manage performance manually. The workload of one volume is going to one rank.
This method makes the identification of performance bottlenecks easier; however,
by putting all the volumes data onto just one rank, you might introduce a
bottleneck, depending on your actual workload.
The DS8000 series uses a volume capacity algorithm (calculation) to provide a
logical unit number (LUN).
In the DS8000 family, physical storage capacities such as DDMs are expressed in
powers of 10. Logical or effective storage capacities (logical volumes, ranks, extent
pools) and processor memory capacities are expressed in powers of 2. Both of these
conventions are used for logical volume effective storage capacities.
On open volumes with 512 byte blocks (including T10-protected volumes), you can
specify an exact block count to create a LUN. You can specify a DS8000 standard
LUN size (which is expressed as an exact number of binary GBs (2^30)) or you can
specify an ESS volume size (which is expressed in decimal GBs (10^9) accurate to
0.1 GB). The unit of storage allocation unit for open volumes is fixed block one
extent. The extent size for open volumes is exactly 1 GB (2^30). Any logical
volume that is not an exact multiple of 1 GB does not use all the capacity in the
last extent that is allocated to the logical volume. Supported block counts are from
1 to 4 194 304 blocks (2 binary TB) in increments of one block. Supported DS8000
sizes are from 1 to 2048 GB (2 binary TB) in increments of 1 GB. The supported
ESS LUN sizes are limited to the exact sizes that are specified from 0.1 to 982.2 GB
(decimal) in increments of 0.1 GB and are rounded up to the next larger 32 K byte
boundary. The ESS LUN sizes do not result in DS8000 standard LUN sizes.
Therefore, they can waste capacity. However, the unused capacity is less than one
full extent. ESS LUN sizes are typically used on DS8000 when volumes must be
copied between DS8000 and ESS.
On open volumes with 520 byte blocks, you can select one of the supported LUN
sizes that are used on System i
uses 8 of the bytes in each block. This leaves 512 bytes per block for your data. The
selected sizes are specified in decimal GB (10^9) or are specified to the exact block
count that is shown in Table 5 on page 39. System i LUNs are defined as protected
or unprotected. If the open volume is defined as unprotected, the AS/400
operating system performs software mirroring on the LUN with another
non-protected internal or external LUN. If the open volume is defined as protected,
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processors to create a LUN. The operating system
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