What does it mean for the reported value of a zvol volsize to be
less than the product of used and compressratio?


For example,

# zfs get -p all home1/home1mm01
NAME             PROPERTY         VALUE                  SOURCE
home1/home1mm01  type             volume                 -
home1/home1mm01  creation         1254440045             -
home1/home1mm01  used             14902492672            -
home1/home1mm01  available        16240062464            -
home1/home1mm01  referenced       14902492672            -
home1/home1mm01  compressratio    11.20x                 -
home1/home1mm01  reservation      0                      default
home1/home1mm01  volsize          161061273600           -
home1/home1mm01  volblocksize     16384                  -
home1/home1mm01  checksum         on                     default
home1/home1mm01 compression gzip-1 inherited from home1
home1/home1mm01  readonly         off                    default
home1/home1mm01  shareiscsi       off                    default
home1/home1mm01  copies           1                      default
home1/home1mm01  refreservation   0                      default



Yet used (14902492672) * compresratio  (11.20) = 166907917926
which is 3.6% larger than volsize.

Is this a bug or a feature for sparse volumes? If a feature, how
much larger than volsize/compressratio can the actual used
storage space grow? e.g., fixed amount overhead and/or
fixed percentage?

Thanks.

--
Stuart Anderson  ander...@ligo.caltech.edu
http://www.ligo.caltech.edu/~anderson



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