gtpd1m1cDatabase Reference

Timing

During capture, entire disk tracks are read at a time by using chained channel control words, including both count and data fields. A search command is not used to check the transfer, but a software check is made when the read is completed to ensure that the proper track has been read. This permits the reading of a track to start after the first address marker is sensed, making rotational delay minimal. One tape record is written for each track of DASD records that is read. The sequence of reading DASD tracks runs from head 0 through the last head on cylinder 0, followed by head 0 through the last head on cylinder 1 and so on for the device that is being captured.

Restore also uses chaining to read a capture tape and write 1 DASD track at a time. The tracks are restored in the sequence previously described for capture. The average rotational delay is about half a disk track. On a restore with the duplicate option, the prime tracks are written to the module concurrently with the duplicates on the duplicate module. If the entire system is being restored, the duplicates are also restored.

Assumptions and Conditions Relative to Timing Example

To simplify timing calculations for a capture and restore operation, certain conditions are assumed and described as follows. These values can be changed to match individual conditions.

  1. It is assumed for this example that a single 3380-D DASD has 50% total tracks allocated and the system is fully duplicated. Because capture copies only the primary copies of duplicated tracks, only half the modules in a system are captured.
  2. 10% of allocated primary DASD tracks each contain ten 4KB records, 30% of DASD tracks each contain thirty 1055-byte records, and 60% of DASD tracks each contain fifty-three 381-byte records.

    This DASD information for a 3380-D is summarized as follows:

    Record Size Records per Track Percent Allocated
    381 bytes 53 60%
    1055 bytes 30 30%
    4096 bytes (4KB) 10 10%
  3. Tape calculations for 3480s and 3490s assume:

    More exact tape timing, using effective data rates expressed in megabytes (MB) per second for 3380-D tracks written out as tape blocks containing 381-, 1055-, and 4096-byte (4KB) record sizes follows:

    Device Type 381-byte Track 1055-byte Track 4096-byte (4KB) Track
    3480 2.35MB per sec 2.5MB per sec 2.5MB per sec
    3490 3.0MB per sec 3.0MB per sec 3.0MB per sec

    The effective data rate values shown include start/stop time and are based on capturing a single disk module at a time to a single tape drive with negligible interference from other system activity.

  4. The amount of time required for switching the tape in a multicartridge capture or restore has not been factored into the estimates.
  5. Tape record size per 3380 DASD track =
      (( nbr records per track ) * ( nbr bytes per record )) + 508
    

    This calculates to the following tape block sizes for the 3380-D to 3480 tape example:

    DASD Tape Block Sizes
    381 bytes 20 702
    1055 bytes 32 162
    4094 bytes (4KB) 41 468
  6. The maximum main storage used by each entry is calculated as follows:
      Total Main Storage per Entry =
        ( 2 * (( nbr 381 records per track  *  381 record size )
            + ( nbr 1055 rcd per trk * 1055 rcd size )
            + ( nbr 4KB rcd per trk * 4KB rcd size ))  )
      + ( nbr work blks * blk size )
    

    At any given time the main storage utilization per entry is the amount of work space used plus the space required for the track size of the device that is being processed.

    For the devices that are being supported, the main storage values are shown as follows:

    Device Work Space 381 Track Space 1055 Track Space 4KB Track Space Total
    3380 8KB (4 blk) 40KB (106 blk) 62KB (60 blk) 80KB (20 blk) 190KB
    3390 8KB (4 blk) 41KB (110 blk) 68KB (66 blk) 96KB (24 blk) 213KB
    9345 8KB (4 blk) 35KB (94 blk) 56KB (54 blk) 80KB (20 blk) 179KB
  7. The system pause time-out factor is the maximum amount of time allowed for an entry to complete after a pause has been requested. Entries exceeding this limit are timed out and aborted. The minimum amount for this field should be at least the maximum time required to capture or restore a module on any in-use device type plus an amount required if the module does not have exclusive use of a channel.
  8. To determine the minimum and maximum rewind and unload time for all tape devices used by capture and restore, do the following:
     (Minimum time = maximum rewind and unload time for the slowest tape device)
                                  +
     (Time needed by the operator; for example, time for mounting the tape)
    

    See the RESCAP macro in TPF System Generation for the default maximum rewind and unload time.

      Tape time per track  =
          ( tape block size per track ) / ( effective data rate )
    

Capture Timing Estimates

The following timing estimates will assist you in calculating your capture and restore time requirements. The assumptions used should be carefully examined to determine if they are correct for a particular system.

Note:
The longer of the disk read and tape write times determines the time required to capture the assumed configuration.

Disk Time Calculations

The following table and calculations show the time required to capture data from the various 3380 DASD models supported by the TPF system.

Average rotational delay is calculated as follows:

  Average Rotational Delay =
 
      ((rotation time / nbr 381 rcds per track) / 2) * (percentage of 381-byte tracks)
   +  ((rotation time / nbr 1055 rcds per track) / 2)) * (percentage of 1055-byte tracks)
   +  ((rotation time / nbr 4K rcds per track) / 2)) * (percentage of 4K-byte tracks)



  Disk time per module  =
 
      ( nbr tracks to capture * ( rotation time + avg rotational delay ))
   +  ( average seek time )
   +  ( cyl-cyl seek time * (( nbr cyl * pct used) - 1 ))

For example:

  3380-D time/mod = 6,638(16.7 + 0.25) + 15 +  3(885*0.5 - 1)  =  117.8 sec.

Tape Time Calculations

The following calculations establish the tape time per captured module. The tables that were shown previously provide supporting information to verify the arithmetic.

Note:
Tape drives use the EDR that is expected for the block size that is being written (32 158-byte blocks for 1055-byte record tracks, 20 701-byte blocks for 381-byte record tracks, and 41 468-byte blocks for 4096-byte record tracks), and the number of records written is the sum of the large, small, and 4KB tracks to capture from the particular device.

Tape time per module = (( nbr bytes per pack ) / ( EDR for tape record size ))

  For 381-byte blocks on 3480:
      3,982 tracks * 20,701 bytes/track / 2.35 MB/sec. = 35 sec.
  For 1055-byte blocks on 3480:
      1,991 tracks * 32,158 bytes/track / 2.5 MB/sec.  = 26 sec.
  For 4KB blocks on 3480:
        664 tracks * 41,468 bytes/track / 2.5 MB/sec.  = 11 sec.
                                                       ___
                               Total tape time        = 72 sec.

The conclusion from these calculations is that the 3380-D DASD example can be captured to 3480 tape in 117.8 seconds, the longer of the 2 timings (72 seconds for tape time and 117.8 seconds for DASD).

Restore Timing Estimates

Single Module Restore Timing Calculations

The following table and calculations show the disk time required to restore 3380 devices. Search time is calculated as follows:

   Search time =  .5 * rotation time + tape read time - disk write time

Tape read time varies for 381-, 1055-, and 4096-byte (4KB) record tracks. This table shows the values as calculated from the effective data rates (EDR) for each record size for both tape drives. Tape time/module is calculated the same as for capture. Restore time is the greater of either tape time/module or disk time/module.

Disk time per module =

  Factor
     I     ( total nbr tracks to restore ) * rotation time
 
    II     + (( tape rd time per 4K rcd trk - write time
                    + ( 0.5 *  rotation time  )) * nbr 4K non-dup trks )
 
   III     + (( tape rd time per 1055 rcd trk - write time
                    + ( 0.5 *  rotation time  )) * nbr 1055 non-dup trks )
 
    IV     + (( tape rd time per 381 rcd trk - write time
                    + ( 0.5 *  rotation time  )) * nbr 381 non-dup trks )
 
     V     +  average seek time
 
    VI     +  ( cyl-cyl seek time * ( nbr cyl per mod  -  1 ))

Nonduplicate Restore:


    FACTOR              I                      II                                  III
 3380 time/mod  =  6638 * (0.0167) + (0.0165 - 0.0167) + (0.0083 * 664) + (0.125 - 0.0167) + (0.0083 * 1992)
                  (0.0085 - 0.0167) + 0.0085 * 3982) + 0.015 + (0.003 * (443 - 1))
                               IV                      V            VI
 
                = 167.3 sec

Duplicate Restore:


    FACTOR              I                      II                                  III
 3380 time/mod  = 13276 * (0.0167) + (0.0165 - 0.0167) + (0.0085 * 1328) + (0.125 - 0.0167) + (0.0085 * 3986)
                  (0.0085 - 0.0167) + 0.0085 * 7964) + 0.015 + (0.003 * (443 - 1))
                               IV                      V            VI
 
                = 333.3 sec

Tape Volume Estimates

The volume of tape produced is calculated as follows:

Length in inches  =   (( nbr bytes transferred ) / ( BPI rate ))
                    + (( IRG size ) * ( nbr records written ))

where:

The following are sample calculations for several 3380-to-tape captures.

Note:
These samples do not take into account any improvements possible with the Increased Data Recording Capability (IDRC) feature available with the 3480 and 3490.
277,045,053/38K + .08(11616) = 8,220 in. = 685 feet (3480 38K BPI)