[rrd-users] Major confusion on RRAs

Sat Jan 4 07:44:05 MET 2003

Since I think I've somewhat figured it out, but still have questions, let me
explain what I know first by example.
Ok, let's say you have an rrd with a 300 second interval that starts at
1041573600 and ends at 1041660000,
which makes a full 24 hours. Then let's say this is the data as follows(this
is kinda long, sorry):

1041573600:0
1041573900:1
1041574200:2
1041574500:3
1041574800:4
1041575100:5
1041575400:6
1041575700:7
1041576000:8
1041576300:9
1041576600:10
1041576900:11
1041577200:12
1041577500:13
1041577800:14
1041578100:15
1041578400:16
1041578700:17
1041579000:18
1041579300:19
1041579600:20
1041579900:21
1041580200:22
1041580500:23
1041580800:24
1041581100:25
1041581400:26
1041581700:27
1041582000:28
1041582300:29
1041582600:30
1041582900:31
1041583200:32
1041583500:33
1041583800:34
1041584100:35
1041584400:36
1041584700:37
1041585000:38
1041585300:39
1041585600:40
1041585900:41
1041586200:42
1041586500:43
1041586800:44
1041587100:45
1041587400:46
1041587700:47
1041588000:48
1041588300:49
1041588600:50
1041588900:51
1041589200:52
1041589500:53
1041589800:54
1041590100:55
1041590400:56
1041590700:57
1041591000:58
1041591300:59
1041591600:60
1041591900:61
1041592200:62
1041592500:63
1041592800:64
1041593100:65
1041593400:66
1041593700:67
1041594000:68
1041594300:69
1041594600:70
1041594900:71
1041595200:72
1041595500:73
1041595800:74
1041596100:75
1041596400:76
1041596700:77
1041597000:78
1041597300:79
1041597600:80
1041597900:81
1041598200:82
1041598500:83
1041598800:84
1041599100:85
1041599400:86
1041599700:87
1041600000:88
1041600300:89
1041600600:90
1041600900:91
1041601200:92
1041601500:93
1041601800:94
1041602100:95
1041602400:96
1041602700:97
1041603000:98
1041603300:99
1041603600:100
1041603900:101
1041604200:102
1041604500:103
1041604800:104
1041605100:105
1041605400:106
1041605700:107
1041606000:108
1041606300:109
1041606600:110
1041606900:111
1041607200:112
1041607500:113
1041607800:114
1041608100:115
1041608400:116
1041608700:117
1041609000:118
1041609300:119
1041609600:120
1041609900:121
1041610200:122
1041610500:123
1041610800:124
1041611100:125
1041611400:126
1041611700:127
1041612000:128
1041612300:129
1041612600:130
1041612900:131
1041613200:132
1041613500:133
1041613800:134
1041614100:135
1041614400:136
1041614700:137
1041615000:138
1041615300:139
1041615600:140
1041615900:141
1041616200:142
1041616500:143
1041616800:144
1041617100:145
1041617400:146
1041617700:147
1041618000:148
1041618300:149
1041618600:150
1041618900:151
1041619200:152
1041619500:153
1041619800:154
1041620100:155
1041620400:156
1041620700:157
1041621000:158
1041621300:159
1041621600:160
1041621900:161
1041622200:162
1041622500:163
1041622800:164
1041623100:165
1041623400:166
1041623700:167
1041624000:168
1041624300:169
1041624600:170
1041624900:171
1041625200:172
1041625500:173
1041625800:174
1041626100:175
1041626400:176
1041626700:177
1041627000:178
1041627300:179
1041627600:180
1041627900:181
1041628200:182
1041628500:183
1041628800:184
1041629100:185
1041629400:186
1041629700:187
1041630000:188
1041630300:189
1041630600:190
1041630900:191
1041631200:192
1041631500:193
1041631800:194
1041632100:195
1041632400:196
1041632700:197
1041633000:198
1041633300:199
1041633600:200
1041633900:201
1041634200:202
1041634500:203
1041634800:204
1041635100:205
1041635400:206
1041635700:207
1041636000:208
1041636300:209
1041636600:210
1041636900:211
1041637200:212
1041637500:213
1041637800:214
1041638100:215
1041638400:216
1041638700:217
1041639000:218
1041639300:219
1041639600:220
1041639900:221
1041640200:222
1041640500:223
1041640800:224
1041641100:225
1041641400:226
1041641700:227
1041642000:228
1041642300:229
1041642600:230
1041642900:231
1041643200:232
1041643500:233
1041643800:234
1041644100:235
1041644400:236
1041644700:237
1041645000:238
1041645300:239
1041645600:240
1041645900:241
1041646200:242
1041646500:243
1041646800:244
1041647100:245
1041647400:246
1041647700:247
1041648000:248
1041648300:249
1041648600:250
1041648900:251
1041649200:252
1041649500:253
1041649800:254
1041650100:255
1041650400:256
1041650700:257
1041651000:258
1041651300:259
1041651600:260
1041651900:261
1041652200:262
1041652500:263
1041652800:264
1041653100:265
1041653400:266
1041653700:267
1041654000:268
1041654300:269
1041654600:270
1041654900:271
1041655200:272
1041655500:273
1041655800:274
1041656100:275
1041656400:276
1041656700:277
1041657000:278
1041657300:279
1041657600:280
1041657900:281
1041658200:282
1041658500:283
1041658800:284
1041659100:285
1041659400:286
1041659700:287
1041660000:288

We'll use the RRA's that were in rrdtutorial:

RRA:AVERAGE:0.5:1:600
RRA:AVERAGE:0.5:6:700
RRA:AVERAGE:0.5:24:775
RRA:AVERAGE:0.5:288:797
RRA:MAX:0.5:1:600
RRA:MAX:0.5:6:700
RRA:MAX:0.5:24:775
RRA:MAX:0.5:288:797

I'm assuming "RRA:AVERAGE:0.5:1:600 (2 days, 2 hours)" will keep 600 (CDPs),
300 second samples, but 24 hours only gives us 288 samples, correct?
I won't bother typing out that RRA since it would just be the same data as
above.

The RRA "RRA:AVERAGE:0.5:6:700 (~12.5 days)" will keep 700 (CDPs), 1500
second samples, which would give us 57.6 samples in 24 hours, right, right?
:D
So, as an example, I would average the following together:

1041573600:0 --
1041573900:1   |
1041574200:2   | - PDPs (?)
1041574500:3   |
1041574800:4 --

(0+1+2+3+4)/5 = 2, so one "RRA:AVERAGE:0.5:6:700" CDP would be 2? Correct?

The RRA "RRA:AVERAGE:0.5:24:775" will keep 775 (CDPs), 7200 second samples,
which would give us 12 samples in 24 hours?!
So, as an example, I would average the following together:

1041573600:0 --
1041573900:1   |
1041574200:2   |
1041574500:3   |
1041574800:4   |
1041575100:5   |
1041575400:6   |
1041575700:7   |
1041576000:8   |
1041576300:9   |
1041576600:10  |
1041576900:11  | - PDPs (?)
1041577200:12  |
1041577500:13  |
1041577800:14  |
1041578100:15  |
1041578400:16  |
1041578700:17  |
1041579000:18  |
1041579300:19  |
1041579600:20  |
1041579900:21  |
1041580200:22  |
1041580500:23--

(0+1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21+22+23)/24 = 11.5,
which would be 1 CDP for "RRA:AVERAGE:0.5:24:775"?

The RRA "RRA:AVERAGE:0.5:288:797" will keep 797 (CDPs), 86400 second
samples, which would give us 1 sample is 24 hours?
So, as an example, I would average the following together:

1041573600 thru 1041660000 ?

 Time for some questions...
  1: Do the RRAs use data from one another, as in, will the RRA
RRA:AVERAGE:0.5:24:775 grab CDPs from RRA:AVERAGE:0.5:288:797
      to come up with it's CDPs?
  2: Why not just use one RRA for the whole year. Ex:
RRA:AVERAGE:0.5:1:105120, I understand that it would cause more
      overhead and a larger RRD, but wouldn't it be more accurate?
  3: For the CF MAX, what would be the point of having multiple RRAs, when
there should be only one MAX in the end? Is that
      to save overhead and space?
  4: If I have the RRAs RRA:AVERAGE:0.5:1:228 and RRA:AVERAGE:5:576 and I
specify more then 24 hours to graph, will it use
      the first or second RRA? what if I graph more then 10 days, will part
of the graph be blank?
  5: What if I specify a higher RRA then the data I will be graphing, will
that affect the graph causing it to show the wrong
      data?
  6: Is there a certain formula to make a perfect RRA for your graph sizes
and times?
  7: If I have a number 3000, and the next interval step the number is 3100,
I use the COUNTER DS, and I want the number
      that's graphed to be a integer. But, the updates might be off a second
or so every once in a while, causing the data to
      become a little off, due to the number being divided by 300, and
getting something subtracted or added due to the time
      being off from the last update. Should I use the GAUGE DS instead, and
have the numbers be parsed before they go to rrdtool,
      causing it to input the difference of 3100 and 3000 instead??
  8: Say your box running rrdtool went down, how would you keep the update
interval from becoming out of sync with the last
      update interval before the box went down?
  9: Which brings me to my final question, is there any way at all to make
sure the updates are done every 5 minutes without
      updating your time against an atomic clock every 2 seconds? :P

Sorry for asking so much and taking so much of you guys' time, it's hard for
me to understand some of this stuff without seeing examples and asking. I
really
appreciate any help anyone gives me! :D (If you guys hate me for sending
this long annoying email, let me know, so I can avoid it in the future :P)

Leo S.

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