Wednesday Apr 22, 2009

Attention with Lustre 1.6.7 and new configuration whitepaper

Lustre 1.6.7 had some serious bugs with the MDT server, and it was withdrawn from the download list. These bugs have been fixed, and a new version 1.6.7.1 has been placed in the download area. If you did download or use Lustre 1.6.7 please upgrade it. Personally, I had a problem in mounting the Lustre filesystem (for both OSS and MDT). After creating the volumes and installing the patches, here on a RedHat CentOS 5.2 machine, I could do the
# mkfs.lustre --fsname lustre --mdt --mgs /dev/vg00n/mdt

but then I could not mount it
# mount -t lustre /dev/vg00/mdt /mdt
mount.lustre: mount /dev/vg00/mdt1 at /mdt failed: No such device
Are the lustre modules loaded?
Check /etc/modprobe.conf and /proc/filesystems
Note 'alias lustre llite' should be removed from modprobe.conf


and there only is a ldiskfs and no lustre  in /proc/filesystems ....
When using Lustre 1.6.6 everything works fine.

Furthermore, there is an excellent whitepaper explaining the configuration and benchmarks of two different hardware setups. The first one uses a Sun Fire X4250 OSS server connected to a Sun Storage J4200 array with 12 300GB SAS drives, while the other uses one Sun Fire X4540 server (THOR) with 48 internal 1TB 7200rpm SATA drives. The first one uses the disk in a RAID0, while the second uses a RAID6 setup. All configuration descriptions include a HA (high availability) version.  Please download this excellent paper from here.

[Read More]

Thursday Mar 19, 2009

Lustre quick start guide is available

As promised in my last blog, Torben Kling's Whitepaper about a step by step Lustre set-up is available now! Please get it from here. This whitepaper explains everything from the installation of Linux, creating the virtual volumes, downloading the Lustre packages, setting up a Metadata server, the Object Store Servers and the clients and finally some examples of managing the file system. Congratulations to Torben for this !
[Read More]

Tuesday Mar 03, 2009

Lustre Parallel File Sytem for CFD analysis Part 2

As already said, Lustre stores files, or blocks of files, that are considered as objects, of one or more OSTs. This is called striping in the Lustre terminology. You will need striping :

- if your file is too large to be stored on a single OST.
- if the required aggregate bandwidth for a single file cannot be offered by a single OST.
- if a client, i.e., your program running on the cluster, needs more bandwidth than a single OSS can offer.

Lustre allows you to configure the number of stripes, the stripesize and the servers (OSS) to use, for every file, directory or directory-tree.

Practically, the smallest recommended stripe size is 512 KB because Lustre tries to batch I/O into 512 KB chunks over the network. This is a good amount of data to transfer at one time.

Perhaps you will see a problem, that the file that you are using is considered as a single object. In this case, the file (or object) is stored on a single OST, i.e., a single disk, and you do not see any performance improvement.[Read More]

Tuesday Feb 24, 2009

Lustre Parallel File Sytem for CFD analysis

Whether you are looking at crash simulations, implicit-explicit computations, or CFD analysis, all computing numerical solutions for very different physical models, they have in common, that the size of the data sets becomes bigger and bigger. This is true for the input data, the temporarily computed scratch files, and the final output data. Generally, I/O times have been considered small compared to the runs times of the solver. This may not be longer true today. Not all ISV codes propose a parallel I/O option, and if, it is not always easy to use.

Look for example at the StarCD input files for StarCD V3, V4 and finally StarCCM+ : The same geometry, a 34M cell case, uses 3.5GB for StarCD V3 .geom file and climbs up to 5.1GB when converted into the V4 .ccmg file (or the CCM+ .sim file).[Read More]
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