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This page gives a broad view of the different storage resources that are available for experiments on Grid5000.
The focus is on Big Data experiments. Advantages and disadvantages will be highlighted to help the user decide on the optimal combination of storage resources. This will help in two directions:
- It will help the user achieve better quality in experiments
- It will avoid excessive usage of any single type of resource by a user, thereby making them available mutually to other users of Grid'5000.
In Grid'5000, there are multiple resources for data storage in experiments. Each has its own characteristics, advantages and disadvantages. They are summarised in the table below. Further details are discussed in the following sub-sections.
Remember that Grid'5000 does NOT have a BACKUP service for storage it provides: it is your responsibility to save important data outside Grid'5000 (or at least to copy data to several Grid'5000 sites in order to increase redundancy).
Comparison table of storage resources
The following table summarises the comparison of different aspects of storage resources on Grid'5000 - both persistent and non-persistent types:
|Storage Resource||Backups?||Protocol used||Persistence period||Provisioning mechanism||Network connectivity||Remarks|
|/home||No||NFS||long-term||Quota + User Acct mgmt||Variable (1Gb/s - 10 Gb/s)||Note-1|
|Group Storage||No||NFS||long-term||Manual||Variable (1Gb/s - 10 Gb/s)||Note-1|
|On node local disks reservation||No||-||medium-term||OAR||-||Note-2, Note-4|
|Managed Ceph cluster||No||RADOS||medium-term||Temporarily free (until contention for space)||~n X 10 Gb/s (n = parallelism)||Note-3|
|/tmp||No||-||short-term (job)||OAR job||-|
|Local disks||No||-||short-term (job)||OAR job||-||Note-4|
- Note-1: These storage resources use NFS accessed by multiple users. Hence, the performance is strongly dependent on the degree of contention during the time of experiment.
- Note-2: This storage uses the hard disks of the reserved node, but allows to reserve disks separately from the node.
- Note-3: There are 2 factors to consider for performance:
- aggregated network bandwidth of all the nodes in the cluster:
- for the managed Ceph Cluster at rennes (4 nodes each with 1 network interface), n = 4,
- for the managed Ceph Cluster at nantes (3 nodes each with 1 network interface), n = 3,
- the aggregated disk bandwidth of all Object Storage Devices (OSD) used in the cluster. The recommendation is to have 1 OSD per physical disk.
- For further interesting details on maximum storage capacity and degree of parallelism in Ceph clusters, see here.
- aggregated network bandwidth of all the nodes in the cluster:
- Note-4: Local disks need to be manually partitioned and formatted with a filesystem
This is the principal storage space when logged-in on a Grid'5000 site:
userid. It is based on File System exposed by NFS.
Every user has a
userid storage in every Grid'5000 site (content is not automatically replicated nor backuped).
- In term or storage size
Each user has a default quota of 25GB of storage on each site (soft limit), with a reserve of 100GB (hard limit).
- the soft limit is set to what the admins find a reasonable limit for an account on a more or less permanent basis. You can use more disk space temporarily, but you should not try and trick the system to keep that data on the shared file system.
- the hard limit is set so as to preserve usability for other users if one of your scripts produces unexpected amounts of data. You'll not be able to override that limit.
We have a limitation of 200GB per home dir, above that threshold you should consider asking for a group storage instead, preferably at the team level since it will be usable/shareable by all of your team mates. If your team does not have yet a group storage, talk about this to your GGA manager.
Should you need higher quotas, please visit your user account settings page at https://api.grid5000.fr/ui/account (homedir quotas tab) at fill a request, or send an email to email@example.com, explaining how much storage space you want and what for.
- In term of storage access
/home is manageable using the Storage Manager.
This service provides large storage spaces, possibly shared between multiple Grid'5000 users. Those storage spaces are accessible on Grid'5000 over NFS. User can ask for a group storage creation by following the procedure described in the Group Storage page.
Advantages: Shareable storage among a group of user, persistent, easy access
Disadvantage: The disadvantages are those of an NFS server with multiple simultaneous users.
This storage space is available under
/srv/osirim/<username> directory from frontends and nodes (in default environment or deployed -nfs and -big). It is provided by the OSIRIM project (IRIT lab) and exposed by NFS (using an autofs mount). Each user has a quota of 200GB of storage. If required, user can request to increase the size of the quota, by sending an email to firstname.lastname@example.org.
Disk reservation consists in reserving extra local hard disks of nodes, in order to locally store large datasets between reservations, and thus avoid the need of moving data to nodes at the beginning of every node reservation. Disk reservation provides medium-term storage persistence.
Advantages: Storage is available directly on the hard disk of the reserved node.
Disadvantage: You need to reserve a hard disk on a node, and then reserve the same node for carrying out your experiment.
These are Object-based storage resources (i.e. not offering a File System interface). They are based in
rennes site (~9 TB) and at
nantes site (~7 TB). Hence, overall they aggregate to ~15 TB of storage resources. For details about Managed Ceph resources see here.
Advantages: Ceph is a distributed object storage system designed to provide excellent performance, reliability and scalability using multiple nodes.
Using Virtual Block Devices with managed Ceph backend: If experiments can support variable performances then the managed Ceph clusters offer additional persistent storage resources. They will be used in this tutorial also. Here is an example of using virtual block devices for creating a persistent Database service on a virtual machine.
Disadvantages: These are Object-based storage: hence non-accessible using direct Unix filesystem commands.