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HPDT Packing is enabled on a TRLE basis. When enabled,
seven packing buffers are acquired for each write device defined in
the TRLE. Packing buffer size does not vary within the TRLE. Packing
buffers are obtained from the smallest CSM data space pool that can
contain the entire buffer. - Determining packing buffer size
- The packing buffer size is equal to the number of 4 KB pages (minus
1 page) specified by the MAXBFRU parameter on the TRLE definition
in the adjacent link station (or equivalent when the adjacent link
station is a router). This value can be determined without accessing
the adjacent link station when the TRLE is active. Issue the DISPLAY
NET,ID=trlename command for the TRLE for which you are considering
enabling HPDT Packing. The MAXBFRU value of the adjacent link station
is contained in the response. The response looks similar to the following
example:
IST097I DISPLAY ACCEPTED
IST075I NAME = TRLE1A, TYPE = TRLE
IST486I STATUS= ACTIV----E, DESIRED STATE= ACTIV
IST087I TYPE = LEASED , CONTROL = MPC , HPDT = YES
IST1715I MPCLEVEL = HPDT MPCUSAGE = SHARE
IST1717I ULPID = AHHCPU1
IST1801I UNITS OF WORK FOR NCB AT ADDRESS X'02EAE018'
IST1802I CURRENT = 0 AVERAGE = 1 MAXIMUM = 2
>IST1577I HEADER SIZE = 4092 DATA SIZE = 16 STORAGE = ***NA***
IST1221I WRITE DEV = 0508 STATUS = ACTIVE STATE = ONLINE
IST1577I HEADER SIZE = 4092 DATA SIZE = 16 STORAGE = DATASPACE
IST1221I READ DEV = 0408 STATUS = ACTIVE STATE = ONLINE
IST314I END
The DATA SIZE value reported in the first IST1577I message reflects
the MAXBFRU parameter in the adjacent link station. In this case,
the adjacent link station defined a data stream maximum size of 16
pages. Therefore, if HPDT Packing is enabled for this TRLE, the packing
buffer size will be 15 pages, or 60 KB. Because 7 packing buffers
are allocated for the single write device, the total storage cost
in CSM fixed data space is 7*60 KB or 420 KB.
- Packing buffer size versus CSM data space pool size
- The packing buffers are obtained from the smallest CSM data space
pool that can contain the entire buffer. If the packing buffer size
does not equal one of the CSM data space pool sizes, storage is wasted.
In the example above, the packing buffer size is exactly equal to
the second largest CSM data space pool size; therefore no storage
is wasted. The worst case occurs when DATA SIZE is equal to 10, meaning
9 page (36 KB) packing buffers are used. Because the packing buffers
cannot be acquired from the 32 KB pool, they are acquired from the
60 KB pool. The last 24 KB of each packing buffer is wasted. 7*24
KB equals 160 KB of wasted storage for a single write device.
The previous example explains why you should adjust the MAXBFRU value
in the adjacent node (if necessary) before enabling HPDT Packing,
so that the packing buffer size is equal to one of the CSM data space
pools sizes.
Table 1 shows the
correlation between DATA SIZE (MAXBFRU in the adjacent link station),
the packing buffer size, the CSM data space pool size from which the
packing buffers are allocated, and any apparent storage waste because
of mismatch of packing buffer size and CSM data space pool size. Table 1. HPDT Packing - packing buffer size, CSM pools
size, and waste per packing bufferDATA SIZE |
Packing buffer size |
CSM pool used |
Waste per packing buffer |
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2 |
4 KB |
4 KB |
None |
3 |
8 KB |
16 KB |
8 KB |
4 |
12 KB |
16 KB |
4 KB |
5 |
16 KB |
16 KB |
None |
6 |
20 KB |
32 KB |
12 KB |
7 |
24 KB |
32 KB |
8 KB |
8 |
28 KB |
32 KB |
4 KB |
9 |
32 KB |
32 KB |
None |
10 |
36 KB |
60 KB |
24 KB |
11 |
40 KB |
60 KB |
20 KB |
12 |
44 KB |
60 KB |
16 KB |
13 |
48 KB |
60 KB |
12 KB |
14 |
52 KB |
60 KB |
8 KB |
15 |
56 KB |
60 KB |
4 KB |
16 |
60 KB |
60 KB |
None |
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