.OBD Statfs
[[struct-obd-statfs]]
****
An 'obd_statfs' structure conveys file-system-wide information of a
given target (MDT or OST).

[source,c]
----
struct obd_statfs {
        __u64  os_type;
        __u64  os_blocks;
        __u64  os_bfree;
        __u64  os_bavail;
        __u64  os_files;
        __u64  os_ffree;
        __u8   os_fsid[40];
        __u32  os_bsize;
        __u32  os_namelen;
        __u64  os_maxbytes;
        __u32  os_state;
        __u32  os_fprecreated;
        __u32  os_spare2;
        __u32  os_spare3;
        __u32  os_spare4;
        __u32  os_spare5;
        __u32  os_spare6;
        __u32  os_spare7;
        __u32  os_spare8;
        __u32  os_spare9;
};
----
****

Most of the fields correspond directly to the 'struct statfs' fields
returned by a 'statfs()' system call and have the same meaning. The
values are for the target in question (MDT or OST).

The 'os_type' field gives the kind of file system used for the
target's OSD:

.File system types ('os_type') for Lustre targets
[options="header"]
|====
| f_type                     | value
| EXT4_SUPER_MAGIC (ldiskfs) | 0xEF53
| ZFS_SUPER_MAGIC            | 0x2fc12fc1
|====

The 'os_blocks' field is the total number of blocks in the target, in
units of os_bsize.

The 'os_bfree' field is the number of blocks not currently in use.

The 'os_bavail' is the number of blocks available to be allocated to
new files.  The number of available blocks is typically lower than the
number of free blocks due to outstanding "grants" (see <<grant>>) and
blocks reserved for target internal usage such as metadata.

The 'os_files' field is the total number of files on the target, both
allocated and free.  For some OSD types this is a static number, and
for others this is dynamic based on os_ffree and the amount of free
space.

The 'os_ffree' field is the current number of files that could be
created based on current usage.  For some OSD types this is a function
of the free space in the device and may increase or decrease as free
space changes.

The 'os_fsid' is intended to be the target backing device UUID in
ASCII format.  The current osd-ldiskfs and osd-zfs implementations
do not fill this field in.

The 'os_bsize' field is the block size in bytes. This is for computing
the total, free, and available space in combination with 'os_blocks',
'os_bfree', and 'os_bavail' respectively.  It does not necessarily
represent the minimum or optimal IO size.

The 'os_namelen' field gives the maximum name length (in bytes) for
files on the OSD.

The 'os_maxbytes' field is the maximum size of a single object
(i.e. the maximum byte offset that can be written to).  This is the
same value as the 'ocd_maxbytes' field of the 'obd_connect_data'
structure.

The 'os_state' field encodes the status of the OSD. It can be:

.OSD state
[options="header"]
|====
| os_state flag     | value
| OS_STATE_DEGRADED | 0x1
| OS_STATE_READONLY | 0x2
|====

In normal operation the 'os_state' value is returned as 0x0.  If the
OSD has a RAID configuration that is degraded or
rebuilding the state is returned with the OS_STATE_DEGRADED (0x1) flag
set. If the file system has been set to read-only, either manually at
mount or automatically due to detected corruption of the underlying
target file system, then 'os_state' is returned with OS_STATE_READONLY (0x2)
set.

The 'os_fprecreated' field counts the number of pre-created objects
available on an OST. The 'os_fprecreated' value counts as "used"
inodes, so it reduces 'os_ffree'. Lustre places a hard limit of
2*OST_MAX_PRECREATE (2*20000) on the number of precreates it will
allow for an OST. There are currently no precreated objects on an MDT
so it is just 0 in that case.