The S figures (66 MB -> 42.0s, two passes agreeing to 0.6s) had a spread tight
enough to prove fixed work dominates, which is exactly why they said nothing about
M. Second point taken 327x larger, same app, same method: clock from restore
request to the app serving the correct discriminator.
rallly's postgres volume grown 66 MB -> 21.1 GB (200k rows, STORAGE EXTERNAL so
TOAST cannot compress it into a fake number). Two reps:
rep 1 backup 406.4s unit 41149 MB RTO 624.5s discriminator correct
rep 2 backup 387.2s unit 41133 MB RTO 591.8s discriminator correct
327x the data cost 14.5x the time - strongly sub-linear:
RTO ~= 40s + 26.9 s/GB backup ~= 29s + 17.4 s/GB
10 GB -> 5.2 min 20 GB -> 9.6 min (measured 10.1) 100 GB -> 46 min
The fixed ~40s dominates below ~1.5 GB, which IS the S band and explains its tight
clustering.
The more consequential result is capacity. A DB-backed app's recovery unit is
1.90x its data (volume tar PLUS SQL dump): 21.1 GB produced a 40.2 GB unit. The
default appliance ships /mnt/sys_drive at 20 GB, so the largest app that can hold
a local Tier-1/2 recovery unit on a default box is about 10 GB - and that fills the
volume. The M band does not fit on a default box at all; this test only reached
21 GB because sys_drive was first grown 20G -> 70G with the same operation the
product performs via SysDataGrowGB. A tier-sizing decision, not a defect, but it
is invisible until an app crosses it.
Caveats stated in the doc: two points define a line but do not test linearity; the
1.90x is DB-app-specific and a file-only app should be nearer 1.0x (inferred, not
measured); synthetic incompressible data; one app, one box.
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