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Commit da85c165 authored by Jan Siwiec's avatar Jan Siwiec
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Update storage.md

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......@@ -261,52 +261,7 @@ It is not recommended to allocate large amount of memory and use large amount of
### Global RAM Disk
The Global RAM disk spans the local RAM disks of all the nodes within a single job.
![Global RAM disk](../img/global_ramdisk.png)
The Global RAM disk deploys
BeeGFS On Demand parallel filesystem, using local RAM disks as a storage backend.
The Global RAM disk is mounted at /mnt/global_ramdisk.
!!! note
The global RAM disk is on-demand. It has to be activated by **global_ramdisk=true** in the qsub command.
```console
$ qsub -q qprod -l select=4,global_ramdisk=true ./jobscript
```
This command would submit 4 node job in qprod queue, once running a 440GB RAM disk shared across the 4 nodes will be created.
The RAM disk will be accessible at /mnt/global_ramdisk, files written to this RAM disk will be visible on all 4 nodes.
The file system is private to a job and shared among the nodes, created when the job starts and deleted at the job end.
!!! note
The Global RAM disk will be deleted immediately after the calculation end. Users should take care to save the output data from within the jobscript.
The files on the Global RAM disk will be equally striped across all the nodes, using 512k stripe size.
Check the Global RAM disk status:
```console
$ beegfs-df -p /mnt/global_ramdisk
$ beegfs-ctl --mount=/mnt/global_ramdisk --getentryinfo /mnt/global_ramdisk
```
Use Global RAM disk in case you need very large RAM disk space. The Global RAM disk allows for high performance sharing of data among compute nodes
within a job.
!!! warning
Be very careful, use of Global RAM disk file system is at the expense of operational memory.
| Global RAM disk | |
| ------------------ | --------------------------------------------------------------------------|
| Mountpoint | /mnt/global_ramdisk |
| Accesspoint | /mnt/global_ramdisk |
| Capacity | (N*110)GB |
| Throughput | 3*(N+1)GB/s, 2GB/s single POSIX thread |
| User quota | none |
N = number of compute nodes in the job.
For more information, see the [Job Features][12] section.
## Summary
......@@ -382,6 +337,7 @@ N = number of compute nodes in the job.
[9]: #shared-workspaces
[10]: ../general/obtaining-login-credentials/obtaining-login-credentials.md
[11]: ../storage/standard-file-acl.md
[12]: ../job-features.md#global-ram-disk
[c]: https://access.redhat.com/documentation/en-US/Red_Hat_Storage/2.0/html/Administration_Guide/ch09s05.html
[d]: https://support.it4i.cz/rt
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