Difference between revisions of "Data accumulation rate"

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This page gives some rules for estimating the accumulation rate of data on disk for a running MCE.
 
This page gives some rules for estimating the accumulation rate of data on disk for a running MCE.
  
−
In general, during a regular acquisition, the data rate of an MCE is:
+
== Rate calculations ==
 +
In general, during a regular acquisition, the data rate (bit rate) of an MCE is:
  
−
:<math>S_w \times N_c \times N_r \times R</math>
+
:''S''<sub>w</sub> &times; (''S''<sub>head</sub> + ''N''<sub>c</sub> &times; ''N''<sub>RC</sub> &times; ''N''<sub>rro</sub> + ''S''<sub>chk</sub>) &times; ''f''<sub>DV</sub>
 +
where:
 +
* ''S''<sub>w</sub> is the word size (=32 bits)
 +
* ''S''<sub>head</sub> is the size (in words) of the [[frame header]] (=43 words)
 +
* ''N''<sub>c</sub> is the number of columns per [[readout card]] (=8)
 +
* ''N''<sub>RC</sub> is the number of readout cards read out (see {{param|cc|rcs_to_report_data}})
 +
* ''N''<sub>rro</sub> is the number of rows read out (i.e. {{param|cc|num_rows_reported}})
 +
* ''S''<sub>chk</sub> is the size (in words) of the frame checksum (=1 word)
 +
* ''f''<sub>DV</sub> is the read-out data rate.  When in internal-DV mode (i.e. {{param|cc|use_dv}} is zero), this is:
 +
::''f''<sub>DV</sub> = 50&nbsp;MHz / (''N''<sub>dr</sub> &times; ''N''<sub>r</sub> &times; ''N''<sub>rl</sub>)
 +
::&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ≡ ''f''<sub>ARZ</sub> / ''N''<sub>dr</sub>
 +
where:
 +
* 50&nbsp;MHz is the clock rate
 +
* ''N''<sub>dr</sub> is the number of samples co-added into an output frame (i.e. {{param|cc|data_rate}})
 +
* ''N''<sub>r</sub> is the number of rows servoed (i.e. {{param|sys|num_rows}})
 +
* ''N''<sub>rl</sub> is the row dwell-time in clock periods (i.e. {{param|sys|row_len}}), and
 +
* ''f''<sub>ARZ</sub> is the Address-return-to-zero rate, i.e. the frequency at which a single pixel is visited
  
−
where:
 
−
* <math>S_w</math> is the word size (=32 bits)
 
−
* <math>N_c</math> is the number of columns read (<math>=8 \times N_{RC}</math>, where <math>N_{RC}</math> is the number of [[readout card]]s used)
 
−
* <math>N_r</math> is the number of rows read
 
−
* <math>R</math> is the read-out data rate
 
  
 
A useful approximation is:
 
A useful approximation is:
 +
* a single readout card reading 41 rows at 400 Hz is ≈ 0.5 megabytes/second.
  
−
: a single readout card reading 41 rows at 400 Hz is <math>\approx0.5</math> megabytes/second.
+
== Tables ==
 +
Here are some tables of accumulation rates for both kinds of subracks for various data rates and numbers of rows:
  
−
Here's are some tables of accumulation rates for a two readout card 48HP subrack (multiply by 2 for a full sized 72HP subrack with 4 readout cards) for various data rates and numbers of rows:
+
{| class="wikitable" style="text-align: right"
 +
|+ MCE data accumulation rate in Megabits per second (Mbps)
 +
|-
 +
! rowspan="2" | &nbsp;
 +
! colspan="4" | 48HP
 +
! rowspan="5" | &nbsp;
 +
! colspan="4" | 72HP
 +
|-
 +
! 100 Hz
 +
! 150 Hz
 +
! 200 Hz
 +
! 400 Hz
 +
! 100 Hz
 +
! 150 Hz
 +
! 200 Hz
 +
! 400 Hz
 +
|-
 +
! 25 rows
 +
| 1.28
 +
| 1.92
 +
| 2.56
 +
| 5.12
 +
| 2.56
 +
| 3.84
 +
| 5.12
 +
| 10.24
 +
|-
 +
! 33 rows
 +
| 1.69
 +
| 2.53
 +
| 3.38
 +
| 6.76
 +
| 3.38
 +
| 5.07
 +
| 6.76
 +
| 13.52
 +
|-
 +
! 41 rows
 +
| 0.94
 +
| 1.42
 +
| 1.89
 +
| 3.78
 +
| 1.42
 +
| 2.83
 +
| 3.78
 +
| 7.56
 +
|}
  
−
{| class="wikitable"
+
 
−
|+ 48HP subrack data accumulation rate in Gigabytes (<math>10^9</math>&nbsp;bytes) per hour
+
{| class="wikitable" style="text-align: right"
 +
|+ MCE data accumulation rate in Gigabytes (10<sup>9</sup>&nbsp;bytes) per hour
 +
|-
 +
! rowspan="2" | &nbsp;
 +
! colspan="4" | 48HP
 +
! rowspan="5" | &nbsp;
 +
! colspan="4" | 72HP
 
|-
 
|-
−
!
 
 
! 100 Hz
 
! 100 Hz
 
! 150 Hz
 
! 150 Hz
 
! 200 Hz
 
! 200 Hz
−
! 300 Hz
 
 
! 400 Hz
 
! 400 Hz
−
! 600 Hz
+
! 100 Hz
 +
! 150 Hz
 +
! 200 Hz
 +
! 400 Hz
 
|-
 
|-
 
! 25 rows
 
! 25 rows
−
| 0.55
+
| 0.58
−
| 0.8
+
| 0.86
−
| 1.1
+
| 1.15
−
| 1.6
+
| 2.30
−
| 2.1
+
| 1.15
−
| 3.2
+
| 1.73
 +
| 2.30
 +
| 4.61
 
|-
 
|-
 
! 33 rows
 
! 33 rows
−
| 0.7
+
| 0.76
−
| 1.1
+
| 1.14
−
| 1.4
+
| 1.52
−
| 2.1
+
| 3.04
−
| 2.8
+
| 1.52
−
| 4.2
+
| 2.28
 +
| 3.04
 +
| 6.08
 
|-
 
|-
 
! 41 rows
 
! 41 rows
−
| 0.9
+
| 2.10
−
| 1.3
+
| 3.15
−
| 1.8
+
| 4.20
−
| 2.6
+
| 8.40
−
| 3.5
+
| 4.20
−
| 5.3
+
| 6.30
 +
| 8.40
 +
| 16.79
 
|}
 
|}
  
  
−
{| class="wikitable"
+
{| class="wikitable" style="text-align: right"
−
|+ 48HP subrack data accumulation rate in Gigabytes (<math>10^9</math>&nbsp;bytes) per day
+
|+ MCE data accumulation rate in Gigabytes (10<sup>9</sup>&nbsp;bytes) per day
 +
|-
 +
! rowspan="2" | &nbsp;
 +
! colspan="4" | 48HP
 +
! rowspan="5" | &nbsp;
 +
! colspan="4" | 72HP
 
|-
 
|-
−
!
 
 
! 100 Hz
 
! 100 Hz
 
! 150 Hz
 
! 150 Hz
 
! 200 Hz
 
! 200 Hz
−
! 300 Hz
 
 
! 400 Hz
 
! 400 Hz
−
! 600 Hz
+
! 100 Hz
 +
! 150 Hz
 +
! 200 Hz
 +
! 400 Hz
 
|-
 
|-
 
! 25 rows
 
! 25 rows
−
| 12.9
+
| 13.8
−
| 19.3
+
| 20.7
−
| 25.7
+
| 27.7
−
| 38.6
+
| 55.3
−
| 51.5
+
| 27.7
−
| 77.2
+
| 41.5
 +
| 55.3
 +
| 110.6
 
|-
 
|-
 
! 33 rows
 
! 33 rows
−
| 17.0
+
| 18.1
−
| 25.5
+
| 27.4
 +
| 36.5
 +
| 73.0
 +
| 36.5
 +
| 54.7
 +
| 73.0
 +
| 146.0
 +
|-
 +
! 41 rows
 +
| 22.7
 
| 34.0
 
| 34.0
−
| 51.0
+
| 45.3
 +
| 90.7
 +
| 45.3
 
| 68.0
 
| 68.0
−
| 102.0
+
| 90.7
−
|-
+
| 181.4
−
! 41 rows
 
−
| 21.1
 
−
| 31.7
 
−
| 42.2
 
−
| 63.3
 
−
| 84.5
 
−
| 126.7
 
 
|}
 
|}
 +
 +
 +
[[Category:Software]]

Latest revision as of 15:20, 5 January 2026

This page gives some rules for estimating the accumulation rate of data on disk for a running MCE.

Rate calculations

In general, during a regular acquisition, the data rate (bit rate) of an MCE is:

Sw × (Shead + Nc × NRC × Nrro + Schk) × fDV

where:

  • Sw is the word size (=32 bits)
  • Shead is the size (in words) of the frame header (=43 words)
  • Nc is the number of columns per readout card (=8)
  • NRC is the number of readout cards read out (see rcs_to_report_data)
  • Nrro is the number of rows read out (i.e. num_rows_reported)
  • Schk is the size (in words) of the frame checksum (=1 word)
  • fDV is the read-out data rate. When in internal-DV mode (i.e. use_dv is zero), this is:
fDV = 50 MHz / (Ndr × Nr × Nrl)
      ≡ fARZ / Ndr

where:

  • 50 MHz is the clock rate
  • Ndr is the number of samples co-added into an output frame (i.e. data_rate)
  • Nr is the number of rows servoed (i.e. num_rows)
  • Nrl is the row dwell-time in clock periods (i.e. row_len), and
  • fARZ is the Address-return-to-zero rate, i.e. the frequency at which a single pixel is visited


A useful approximation is:

  • a single readout card reading 41 rows at 400 Hz is ≈ 0.5 megabytes/second.

Tables

Here are some tables of accumulation rates for both kinds of subracks for various data rates and numbers of rows:

MCE data accumulation rate in Megabits per second (Mbps)
  48HP   72HP
100 Hz 150 Hz 200 Hz 400 Hz 100 Hz 150 Hz 200 Hz 400 Hz
25 rows 1.28 1.92 2.56 5.12 2.56 3.84 5.12 10.24
33 rows 1.69 2.53 3.38 6.76 3.38 5.07 6.76 13.52
41 rows 0.94 1.42 1.89 3.78 1.42 2.83 3.78 7.56


MCE data accumulation rate in Gigabytes (109 bytes) per hour
  48HP   72HP
100 Hz 150 Hz 200 Hz 400 Hz 100 Hz 150 Hz 200 Hz 400 Hz
25 rows 0.58 0.86 1.15 2.30 1.15 1.73 2.30 4.61
33 rows 0.76 1.14 1.52 3.04 1.52 2.28 3.04 6.08
41 rows 2.10 3.15 4.20 8.40 4.20 6.30 8.40 16.79


MCE data accumulation rate in Gigabytes (109 bytes) per day
  48HP   72HP
100 Hz 150 Hz 200 Hz 400 Hz 100 Hz 150 Hz 200 Hz 400 Hz
25 rows 13.8 20.7 27.7 55.3 27.7 41.5 55.3 110.6
33 rows 18.1 27.4 36.5 73.0 36.5 54.7 73.0 146.0
41 rows 22.7 34.0 45.3 90.7 45.3 68.0 90.7 181.4
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