Date: Thu, 20 Apr 2017 07:31:23 -0700 From: Kirk McKusick <mckusick@mckusick.com> To: Maxim Sobolev <sobomax@freebsd.org> Cc: FreeBSD Filesystems <freebsd-fs@freebsd.org> Subject: Re: UFS snapshot "file" is slightly bigger than underlying disk partition Message-ID: <201704201431.v3KEVN59061503@chez.mckusick.com> In-Reply-To: <CAH7qZfs4oBdtvJEir95eHkTeVm%2BTPO59%2Bz2L1n0pXj4o3fB9Ww@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
> From: Maxim Sobolev <sobomax@freebsd.org> > Date: Thu, 20 Apr 2017 02:39:12 -0700 > Subject: UFS snapshot "file" is slightly bigger than underlying disk par= tition > To: FreeBSD Filesystems <freebsd-fs@freebsd.org>, > Kirk McKusick <mckusick@mckusick.com> > = > Hi Kirk, > = > I've noticed that the snapshot file is slightly bigger than underlying d= isk > partition. First I thought it's some kind of header attached to the end, > but the size of difference is actually dependent on the disk size. Is it= by > design, or some sort of "off by x" error? What's annoying about that is > that the size is not multiple of SECTOR_SIZE. Also looks like if I just = cut > that junk out resulting FS image is just as usable. > = > Attached script illustrates that. The first column is size of the > partition, the second column is the size of the difference, both in byte= s. > = > 1048576 48 > 2097152 56 > 4194304 72 > 8388608 72 > 16777216 72 > 33554432 72 > 67108864 72 > 134217728 72 > 268435456 72 > 536870912 72 > 1073741824 72 > 2147483648 72 > 4294967296 96 > 8589934592 152 > 17179869184 256 > 34359738368 464 > 68719476736 880 > 137438953472 1720 > 274877906944 3392 > 549755813888 6744 > = > Please advise, thanks. > = > -Max > (P.S. This is 11.0-RELEASE-p9) The extra space is for auxilary information that is used to track changes made in the snapshot. Removing it will cause your snapshot maintainance to slow down by 10-100x and in the worst case can cause it to become corrupt. In short, don't mess with it. Kirk McKusick
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201704201431.v3KEVN59061503>