Bug #430
open
zfs create -b and -o volblocksize produce inconsistent results
0%
Description
libzfs fails to look for a string value for ZFS_PROP_VOLBLOCKSIZE in several places, so only -b should work correctly. However, -b creates volumes with the wrong size while -o volblocksize volumes have the right size.
From IRC:
zfs create -b 512 -o dedup=off -o compression=off -o logbias=latency -o sync=standard -o copies=1 -V 50GB tank/test512minusb zfs create -V 50GB -o dedup=off -o compression=off -o logbias=latency -o sync=standard -o copies=1 -o volblocksize=512 tank/test512volblocksize tank/test512minusb 75.2G 831G 23.9K - tank/test512volblocksize 51.6G 808G 23.9K -
Related issues
Updated by Albert Lee about 13 years ago
- Subject changed from zfs create -o volblocksize is broken to zfs create -b and -o volblocksize produce inconsistent results
Updated by Emmanuel Hocdet about 13 years ago
Volume refreservation would be size+size/volblocksize*checksum size(256)
it's ok for -b
but with -o volblocksize the size for cheksums are always compute as if volblocksize=8k
Updated by Ryan W about 13 years ago
Emmanuel Hocdet wrote:
Volume refreservation would be size+size/volblocksize*checksum size(256)
it's ok for -b
but with -o volblocksize the size for cheksums are always compute as if volblocksize=8k
But for a 50GB ZVOL you end up with 100/131072 = .000762 .. so is that 76GB? Why would a 50GB ZVOL need to be 50% larger than the provisioned size? All checksumming?
In otherwords, you are saying -b acts appropriately but -o volblocksize is the one that's actually broken?
Updated by Ryan W about 13 years ago
This math also doesn't work right for other block sizes unless I'm doing it wrong.
50GB zvol
That's 100GB for the equation:
107 374 182 400/8192*256 or (2097152) = 51200 (or roughly 50GB) (this one is about spot on)
107 374 182 400/64K*256 or (65536*256=16777216) = 64000 (or roughly 62.5GB?)
But a 50GB volume with 64K blocksize comes out to 50.2GB not 62.5GB
Unless I'm doing something wrong.
Updated by Emmanuel Hocdet about 13 years ago
50/512*(512+256) = 75
50/8192*(8192+256) = ~51.6
if you try 64k
50/65536*(65536+256) = ~50.2
-o volblocksize look very strange
Updated by Ryan W about 13 years ago
Emmanuel Hocdet wrote:
50/512*(512+256) = 75
50/8192*(8192+256) = ~51.6
if you try 64k
50/65536*(65536+256) = ~50.2-o volblocksize look very strange
That seems like an entirely different calculation.
Before you said size+size/blocksize*checksum
Now you are using size/block size*(blocksize+checksum)
No wonder my calculations were broken.
Updated by Emmanuel Hocdet about 13 years ago
yep different formula same result
50+50/65536*256 = ~50.2
Updated by Richard Elling about 13 years ago
-b is correct, -o volblocksize is incorrect. See bug #437