Comment #13 on issue 256 by [email protected]: DRBD Volume above 4TB not
working
https://code.google.com/p/ganeti/issues/detail?id=256
I've searched what is the good size to have for metadata disk and it's
really well explained on linbit drbd documentation:
http://drbd.linbit.com/users-guide-8.4/ch-internals.html#s-meta-data-size
So their estimation calcul is really corrrect even if we could use the
exact calcul.
The maximum overrate by estimation is < 1Mb.
So their estimation is that a volume of X megabytes need a medata disk size
of Y megabytes like Y=X/32768+1
Some results as example (with 1Mb minimum due by estimation)
1 Gb => 1 Mb
10 Gb => 1Mb
100 Go => 4Mb
1To => 33Mb
4To => 129Mb
10 To => 321 Mb
16 To => 513 Mb
So actually ganeti use a 128Mb metadata disk size that limit disk size to
~4 Tb and waste a lot of medata for little disk size that are really common
in real usage.
So a great patch would be to use this formula to calculate the metadata
disk size instead the 128Mb fixed size that waste disk storage and limit
disk size to ~4To.
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