Lustre 1.6 Operations Manual

25.3.3 Creating a File on a Specific OST
You can use lfs setstripe to create a file on a specific OST. In the following
example, the file "bob" will be created on the first OST (id 0).
$ lfs setstripe --count 1 --index 0 bob
$ dd if=/dev/zero of=bob count=1 bs=100M
1+0 records in
1+0 records out
$ lfs getstripe bob
OBDS:
0: home-OST0000_UUID ACTIVE
[...]
bob
obdidx objid objid group
0 33459243 0x1fe8c2b 0
25.4 Free Space Management
In Lustre 1.6, the MDT assigns file stripes to OSTs based on location (which OSS)
and size considerations (free space) to optimize filesystem performance. Emptier
OSTs are preferentially selected for stripes, and stripes are preferentially spread out
between OSSs to increase network bandwidth utilization. The weighting factor
between these two optimizations is user-adjustable.
There are two stripe allocation methods, round-robin and weighted. The allocation
method is determined by the amount of free-space imbalance on the OSTs. The
weighted allocator is used when any two OSTs are imbalanced by more than 20%.
Until then, a faster round-robin allocator is used. (The round-robin order maximizes
network balancing.)
25-8 Lustre 1.6 Operations Manual • September 2008