Optimizing storage performance
What to avoid
Avoid having a large number of files in a single directory and rather split files in multiple sub-directories.
statoperations because it can create a significant load on the file system.
Do not use
ls -lon large directories, because it can be slow. Rather use
ls -lonly for the specific files you need extended information about.
Lustre file system (Betzy and Fram)
To get best throughput on the scratch file system (
/cluster/work), you may
need to change the data striping. Striping shall be adjusted based on the
client access pattern to optimally load the object storage targets (OSTs).
On Lustre, the OSTs are referring to disks or storage volumes constructing the
whole file system.
stripe_count indicates how many OSTs to use.
stripe_size indicates how much data to write to one OST before moving to
the next OST.
Striping will only take affect only on new files, created or copied into the specified directory or file name.
/clusterfile system on Fram is 1.
Betzy is implementing Progressive File Layouts to dynamically set file stripe size based on file size growth.
For more detailed information on striping, please consult the Lustre documentation.
Betzy: Progressive File Layouts
PFL removes the need to explicitly specify striping for each file, assigning different Lustre striping characteristics to contiguous segments of a ﬁle as it grows. Dynamic striping allows lower overhead for small files and assures increased bandwidth for larger files. However, note that for workloads with signiﬁcant random read phases it is best to manually assign stripe size and count.
Betzy: Data on Metadata
Lustre file system performance is optimized for large files. To balance that, data on metadata (DoM) is enabled on Betzy to ensure higher performance in case of frequently accessed small files. Files accessed with a size of 2KB or smaller will be stored on a very fast NVMe JBOD directly connected to the metadata servers.
How to find out the current striping
To see the current stripe size (in bytes), use
lfs getsripe [file_system, dir, file]
$ lfs getstripe example.txt example.txt lmm_stripe_count: 1 lmm_stripe_size: 1048576 lmm_pattern: raid0 lmm_layout_gen: 0 lmm_stripe_offset: 75 obdidx objid objid group 75 54697336 0x3429d78 0
Rules of thumb to set stripe counts
For best performance we urge you to always profile the I/O characteristics of your HPC application and tune the I/O behavior.
Here is a list of rules you may apply to set stripe count for your files:
files smaller than 1 GB: default striping
files size between 1 GB - 10 GB: stripe count 2
files size between 10 GB - 1 TB: stripe count 4
files bigger than 1 TB: stripe count 8
For large files it is advisable to increase stripe count and perhaps chunk size, too. e.g.:
# stripe huge file across 8 OSTs $ lfs setstripe --stripe-count 8 "my_file" # stripe across 4 OSTs using 8 MB chunks. $ lfs setstripe --stripe-size 8M --stripe-count 4 "my_dir"
It is advisable to use higher stripe count for applications that write to a single file from hundreds of nodes, or a binary executable that is loaded by many nodes when an application starts.
Choose a stripe size between 1 MB and 4 MB for sequential I/O. Larger than 4 MB stripe size may result in performance loss in case of shared files.
Set the stripe size a multiple of the write() size, if your application is writing in a consistent and aligned way.
For many small files and one client accessing each file, change stripe count to 1. Avoid having small files with large stripe counts. This negatively impacts the performance due to the unnecessary communication to multiple OSTs.
$ lfs setstripe --stripe-count 1 "my_dir"
BeeGFS filesystem (Saga)
Striping in BeeGFS (
/cluster) cannot be re-configured on Saga by users, it can currently
only be modified by system administrators.
But one thing you can do is to check the current stripe size (here for an example file):
$ beegfs-ctl --getentryinfo example.txt Entry type: file EntryID: 55-628B3E1D-144 Metadata node: mds3-p2-m4 [ID: 324] Stripe pattern details: + Type: RAID0 + Chunksize: 512K + Number of storage targets: desired: 4; actual: 4 + Storage targets: + 1203 @ oss-4-1-stor2 [ID: 12] + 2101 @ oss-4-2-stor1 [ID: 21] + 2102 @ oss-4-2-stor1 [ID: 21] + 2103 @ oss-4-2-stor1 [ID: 21]
This shows that this particular file is striped over 4 object storage targets.