Handling Full OSTs

Sometimes the file system becomes unbalanced, often due to changed stripe settings. If an OST is full and an attempt is made to write more information to the file system, an error occurs.

The example below shows an unbalanced file system:

[root@LustreClient01 ~]# lfs getstripe /mnt/lustre/test_2
OBDS:
0: lustre-OST0000_UUID ACTIVE
1: lustre-OST0001_UUID ACTIVE
2: lustre-OST0002_UUID ACTIVE
3: lustre-OST0003_UUID ACTIVE
4: lustre-OST0004_UUID ACTIVE
5: lustre-OST0005_UUID ACTIVE
/mnt/lustre/test_2
obdidx objidobjid group
2 80x80
root@LustreClient01 ~]# lfs df -h
UUID bytes Used Available Use% Mounted on
lustre-MDT0000_UUID 4.4G 214.5M 3.9G 4% /mnt/lustre[MDT:0]
lustre-OST0000_UUID 2.0G 751.3M 1.1G 37% /mnt/lustre[OST:0]
lustre-OST0001_UUID 2.0G 755.3M 1.1G 37% /mnt/lustre[OST:1]
lustre-OST0002_UUID 2.0G 1.7G 155.1M 86% /mnt/lustre[OST:2] <-
lustre-OST0003_UUID 2.0G 751.3M 1.1G 37% /mnt/lustre[OST:3]
lustre-OST0004_UUID 2.0G 747.3M 1.1G 37% /mnt/lustre[OST:4]
lustre-OST0005_UUID 2.0G 743.3M 1.1G 36% /mnt/lustre[OST:5]
filesystem summary: 11.8G 5.4G 5.8G 45% /mnt/lustre

In this case, OST:2 is almost full and when one tries to write additional information to the file system (even with uniform striping over all the OSTs), the write command fails as follows:

[root@LustreClient01 ~]# lfs setstripe /mnt/lustre 4M 0 -1 [root@LustreClient01 ~]# dd if=/dev/zero of=/mnt/lustre/test_3 bs=10M count=100 dd: writing `/mnt/lustre/test_3': No space left on device 98+0 records in 97+0 records out 1017192448 bytes (1.0 GB) copied, 23.2411 seconds, 43.8 MB/s 16 Lustre File System: Demo Quick Start Guide Sun Microsystems, Inc. To enable continued use of the file system, the full OST has to be taken offline or, more specifically, rendered read-only. This can be accomplished using the lctl command. Note – This action has to be done on the MDS, since this is the server that allocates space for writing: 1.Log in to the MDS server: 2.Use the lctl dl command to show the status of all file system components: 3.Use the lctl deactive command to take the full OST offline: 4.Again, display the status of the file system components: As can be seen from the device list, OST2 is now inactive. If a new file is now written to the file system, the write will be successful as the stripes are allocated across all the other active OSTs.