Prestaging Data In Cache - HPE XP7 User Manual

Bind mode provides the following advantages over priority mode:
The accessibility of read data is the same as Cache Residency priority mode.
Write operations do not have to wait for available cache segments.
There is no back-end contention caused by destaging data.
The required total cache capacity for bind mode is:
standard cache + Cache Residency cache
Cache Residency bind data that has write attributes is normally not destaged. However, the data
is destaged to disk in the following cases:
During cache blockage that is caused by certain maintenance operations (for example,
cache upgrades) or by cache failure.
When the storage system is powered off.
When the volume is deleted from Cache Residency bind mode.
The next table specifies the cache requirements for bind mode operations. Meeting these
requirements is important for preventing performance degradation. For more information about
calculating cache size for bind mode, see
Table 25 Bind mode cache requirements
System Type
Open systems
Mainframe (for
example, 3390-3,
3390-9)

Prestaging data in cache

Normally, the Cache Residency data is staged into the Cache Residency cache at the first access
from the host. From the second access, cache hit can be done. By using the Cache Residency
"Estimating cache size for Cache Residency" (page
RAID Level or Capacity Specifications
Volume Type
RAID 5 (3390) or RAID Slot capacity: 264 KB
6
Cache segment capacity: 16.5 KB
Cache segments needed per slot: 48
(slot capacity / cache segment
capacity)
RAID 1, or external Slot capacity: 264 KB
volumes
Cache segment capacity: 16.5 KB
Cache segments needed per slot: 32
(slot capacity / cache segment
capacity)
RAID 5 mainframe or Slot capacity: 66 KB
RAID 6
Cache segment capacity: 16.5 KB
Cache segments needed per slot: 12
(slot capacity / cache segment
capacity)
Note: Even though a mainframe track
is 56 KB, because cache is divided
into 16.5 KB segments, it requires 4
segments.
RAID 1 mainframe, or Slot capacity: 66 KB
external volumes
Cache segment capacity: 16.5 KB
Cache segments needed per slot: 8
(slot capacity / cache segment
capacity)
Cache Residency Cache
Requirement
3 times the space required
for user data: 1 slot = 3 × 264
KB = 792 KB = 48 cache
segments
2 times the space required
for user data: 1 slot = 2 × 264
KB = 528 KB = 32 cache
segments
3 times the space required
for user data: 1 slot = 3 × 66
KB = 198 KB = 12 cache
segments
2 times the space required
for user data: 1 slot = 2 × 66
KB = 132 KB = 8 cache
segments
Overview of Cache Residency 139
140).