Lustre 1.6 Operations Manual

10.3 Creating an External Journal
While writing large sequential data, small I/O writes are done to update metadata.
This small-sized I/O can affect performance of large sequential I/O with disk seeks.
To avoid metadata operations impacting data throughput, it is advisable to create an
external journal for each OST.
The journal itself is mostly written linearly. As the journal size is almost equal to the
RAM usage, we do not recommend making it large unless there is enough RAM for
the backup.
To create an external journal:
1. On the MDS, perform these steps:
a. Create a 400 MB (or larger) journal partition.
$ sfdisk -uC /dev/sdc ,50,L
> EOF
b. Create a journal device.
$ mke2fs -b 4096 -O journal_dev /dev/sdc1
c. Create the MDT.
$ mkfs.lustre --mdt --mgs --fsname lustre \
--mkfsoptions="-J device=/dev/sdc1" /dev/sdd
d. Mount the MDT.
$ mount -t lustre /dev/sdd /mnt/mds
Chapter 10 RAID 10-13