Hello Eric,
Friday, June 9, 2006, 5:06:49 PM, you wrote:
ES> On Thu, Jun 08, 2006 at 10:53:06PM -0500, Spencer Shepler wrote:
>>
>> On Thu, Eric Schrock wrote:
>> > The problem is that statvfs() only returns two values (total blocks and
>> > free blocks) from which we have to calculate three values: size, free,
>>
>> ?
>>
>> >From statvfs(2) the following are returned in struct statvfs:
>>
>> fsblkcnt_t f_blocks; /* total # of blocks on file system
>> in units of f_frsize */
>> fsblkcnt_t f_bfree; /* total # of free blocks */
>> fsblkcnt_t f_bavail; /* # of free blocks avail to
>>
>> So, the data is being passed back. Is there something I am missing?
ES> Yes, because these values aren't as straightforward as they seem. For
ES> example, consider the return values from UFS:
ES> $ truss -t statvfs -v statvfs df -h /
ES> statvfs64("/", 0x080479BC) = 0
ES> bsize=8192 frsize=1024 blocks=8068757 bfree=2258725
ES> bavail=2178038 files=972608 ffree=809612 favail=809612
ES> fsid=0x1980000 basetype=ufs namemax=255
ES> flag=ST_NOTRUNC
ES> fstr=""
ES> Filesystem size used avail capacity Mounted on
ES> /dev/dsk/c1d0s0 7.7G 5.5G 2.1G 73% /
ES> $
ES> Notice that the values don't correspond to your assumption. In
ES> particular, 'bfree + bavail != blocks'. The two values for 'bfree' and
ES> 'bavail' are used for filesystems that have a notion of 'reserved'
ES> blocks, i.e. metadata blocks which are used by the filesystem but not
ES> available to the user in the form of free space. That's why you have
ES> two values, and if you look at the source code for df(1), you'll see
ES> that it never uses 'bfree' (except in rare internal calculations)
ES> because it's basically useless.
>> So, from the comments, that bit of df code seems to be adjusting
>> for quotas if they exist? I am not sure I understand why
>> zfs' VFS_STATVFS() function can't do what the df command is doing
>> and then return the appropriate value to both df and the NFS server?
>>
>> So, in Robert's case, is that 17GB really available and if so that
>> would seem to be an important thing to report to the NFS clients.
ES> Because as mentioned above, 'free' and 'avail' are really variations on
ES> the same theme. And ZFS _must_ report them as the same value (because
ES> metadata is accounted in the same way as data), so we're constrained by
ES> the POSIX interface.
I haven't been looking into a code (no time lately) but what I'm most
concerned is reported SIZE of a filesystem as it's beeing reported
smaller than it actually is. If snapshots reffered space would be
accounted to free/available space of a filesystem it would be ok.
But changing disk size just because we use snapshots is strange at
least.
But probably I'm still missing something.
Or maybe at least on Solaris<->Solaris we could make it right as
someone else suggested?
--
Best regards,
Robert mailto:[EMAIL PROTECTED]
http://milek.blogspot.com
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