Stuart Anderson
2009-Oct-17 19:47 UTC
[zfs-discuss] zvol used apparently greater than volsize for sparse volume
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 anderson at ligo.caltech.edu http://www.ligo.caltech.edu/~anderson
Cindy Swearingen
2009-Oct-20 15:57 UTC
[zfs-discuss] zvol used apparently greater than volsize for sparse volume
Hi Stuart, The reason why "used" is larger than the volsize is because we aren''t accounting for metadata, which is covered by this CR: http://bugs.opensolaris.org/bugdatabase/view_bug.do?bug_id=6429996 6429996 zvols don''t reserve enough space for requisite meta data Metadata is usually only a small percentage. Sparse-ness is not a factor here. Sparse just means we ignore the reservation so you can create a zvol bigger than what we''d normally allow. Cindy On 10/17/09 13:47, Stuart Anderson wrote:> 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 anderson at ligo.caltech.edu > http://www.ligo.caltech.edu/~anderson > > > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss at opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Stuart Anderson
2009-Oct-20 16:17 UTC
[zfs-discuss] zvol used apparently greater than volsize for sparse volume
Cindy, Thanks for the pointer. Until this is resolved, is there some documentation available that will let me calculate this by hand? I would like to know how large the current 3-4% meta data storage I am observing can potentially grow. Thanks. On Oct 20, 2009, at 8:57 AM, Cindy Swearingen wrote:> Hi Stuart, > > The reason why "used" is larger than the volsize is because we > aren''t accounting for metadata, which is covered by this CR: > > http://bugs.opensolaris.org/bugdatabase/view_bug.do?bug_id=6429996 > 6429996 zvols don''t reserve enough space for requisite meta data > > Metadata is usually only a small percentage. > > Sparse-ness is not a factor here. Sparse just means we ignore the > reservation so you can create a zvol bigger than what we''d normally > allow. > > Cindy > > On 10/17/09 13:47, Stuart Anderson wrote: >> What does it mean for the reported value of a zvol volsize to be >> less than the product of used and compressratio? >>-- Stuart Anderson anderson at ligo.caltech.edu http://www.ligo.caltech.edu/~anderson
Cindy Swearingen
2009-Oct-21 16:54 UTC
[zfs-discuss] zvol used apparently greater than volsize for sparse volume
Hi Stuart, I ran various forms of the zdb command to see if I could glean the metadata accounting stuff but it is beyond my mere mortal skills. Maybe someone else can provide the right syntax. Cindy On 10/20/09 10:17, Stuart Anderson wrote:> Cindy, > Thanks for the pointer. Until this is resolved, is there some > documentation > available that will let me calculate this by hand? I would like to know > how large > the current 3-4% meta data storage I am observing can potentially grow. > > Thanks. > > > On Oct 20, 2009, at 8:57 AM, Cindy Swearingen wrote: > >> Hi Stuart, >> >> The reason why "used" is larger than the volsize is because we >> aren''t accounting for metadata, which is covered by this CR: >> >> http://bugs.opensolaris.org/bugdatabase/view_bug.do?bug_id=6429996 >> 6429996 zvols don''t reserve enough space for requisite meta data >> >> Metadata is usually only a small percentage. >> >> Sparse-ness is not a factor here. Sparse just means we ignore the >> reservation so you can create a zvol bigger than what we''d normally >> allow. >> >> Cindy >> >> On 10/17/09 13:47, Stuart Anderson wrote: >>> What does it mean for the reported value of a zvol volsize to be >>> less than the product of used and compressratio? >>> > > -- > Stuart Anderson anderson at ligo.caltech.edu > http://www.ligo.caltech.edu/~anderson > > >