Re: Same size drive has less usable space

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Thu, Dec 20, 2018 at 10:10:42AM -0600, Eric Sandeen wrote:
> On 12/20/18 9:13 AM, Luciano ES wrote:
> > I have a new drive for backups. 
> > I copied everything over and now I have this problem:
> > 
> > Filesystem      Size  Used 	 Avail 	Use% 	Mounted on
> > /dev/sda1   	931G  914G   18G  	99% 	/xx
> > /dev/sdb1   	931G  920G   11G  	99% 	/xxbkp
> > 
> > So 914GB from the old drive expand and become 920GB. The new drive 
> > is supposed to be the same size, but for some reason it can't 
> > really hold it all. I will be forced to waste precious gigabytes.
> > 
> > I tried to format the new one exactly like the old one, but 
> > it was not possible:
> > 
> > $ xfs_info /xx
> > meta-data=/dev/sda1     isize=256    agcount=8, agsize=30506944 blks
> >          =              sectsz=4096  attr=2, projid32bit=1
> >          =              crc=0        finobt=0 spinodes=0 rmapbt=0
> >          =              reflink=0
> > data     =              bsize=4096   blocks=244055552, imaxpct=25
> >          =              sunit=0      swidth=0 blks
> > naming   =version 2     bsize=4096   ascii-ci=0 ftype=0
> > log      =internal      bsize=4096   blocks=119167, version=2
> >          =              sectsz=4096  sunit=1 blks, lazy-count=1
> > realtime =none          extsz=4096   blocks=0, rtextents=0
> > 
> > 
> > $ xfs_info /xxbkp
> > meta-data=/dev/sdb1     isize=512    agcount=8, agsize=61013888 blks
> >          =              sectsz=512   attr=2, projid32bit=1
> >          =              crc=1        finobt=1 spinodes=1 rmapbt=0
> >          =              reflink=0
> > data     =              bsize=2048   blocks=488111104, imaxpct=25
> >          =              sunit=0      swidth=0 blks
> > naming   =version 2     bsize=4096   ascii-ci=0 ftype=1
> > log      =internal      bsize=2048   blocks=238335, version=2
> >          =              sectsz=512   sunit=0 blks, lazy-count=1
> > realtime =none          extsz=4096   blocks=0, rtextents=0
> > 
> > 
> > I guess at least part of the problem is CRC enabled in the second 
> > one. So, is there anything I can do to make all the data fit in the 
> > new drive?
> 
> Well, you have larger inodes on xxbkp for starters.  If you want,
> 
> # mkfs.xfs -m crc=0,finobt=1 -i sparse=0 -n ftype=0
> 
> should get you the same geometry.  This is all documented in the mfks.xfs
> manpage, btw.
> 
> But beware that copying sparse files w/o maintaining sparseness (for example)
> will also consume more space.  If you want a nothing less than a bit-for-bit
> copy, use dd.  ;)

Why not xfs_copy?

--D

> -Eric