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Disk reservation consists in reserving on nodes hard disks, in order to locally store large datasets between your reservations, and avoid needing moving data to nodes at the beginning of each host reservation. Typically, you can reserve disks for several days, store your data on those disks during your first host reservation, and then access the data during the subsequent reservations.
The table below shows the cluster compatibility with disk reservation.
|Site||Cluster||Number of nodes||Number of reservable disks per node|
- 1 How it works
- 2 Usage
- 3 Show and use my reserved disks
- 4 Security issues
How it works
Two use cases of the disk reservsation are possible:
- long run reservations of disks only (job reserving no host, i.e. no processing power): disk-only reservations do not have to fit in the day vs. night&week-end host reservation policy, and can last up to many days (see Grid5000:UsagePolicy). The reserved disks can then be used by regular host jobs during the period of time of the disk reservation. In this use case, the goal is to get more persistence for the local storage of nodes, e.g. avoid the need to reformat disks and reimport dataset in each regular host job. Those long run jobs must use the
noopOAR job type.
- regular jobs reserving both host and disks. In this use case, the goal is to get access to the reservable disks within the experiment, just as if the disk were not to reserve separately.
In both cases, making use of the reserved disks requires to gain the root privileges, since disks are provided as bare metal hardware to be partitioned, formated, mounted, filled with no restriction but by the experimenter. As a result, the experimenter can use the reserved disk:
- either in a deploy job, in a kadeployed environment (use the
deployOAR job type, then
- or in a non-deploy job, in the standard environment but after enabling sudo with the
Technically speaking, when a deploy job starts, or whenever
sudo-g5k is called in a non-deploy job, the reserved disks stay available while the other disks are disabled. Reserved disks can only be accessed by the user who reserved them.
Please note that reserved disks are not cleaned-up at the end of reservation. As a result:
- Data let on the disks can be accessed by user in later reservations.
- Reserved disk may first need to get cleaned-up before use (remove previous formating and partitioning)
See also Security issues.
The main commands to reserve disks are given below.
Note that accessing the data stored on reserved disks on nodes is only possible with reservation of type deploy (
The maximum duration of a disk reservation is defined in the Usage Policy.
Reserve disks and nodes at the same time
In the 3 following examples, remove the
- How to reserve a node with only the main disk (none of the additional disks), on the grimoire cluster
(no change to the way a node was to be reserved in the past, before the disk reservation mechanism existed.)
- How to reserve a node with all its disks
- How to reserve nodes grimoire-1 and grimoire-2 with one reservable disk per node
Yes, the syntax of the last oarsub command is a bit awkward, so please be careful and mind having:
Reserve disks and nodes separately
You may, for example, decide to reserve some disks for one week, but the nodes where your disks are located only when you want to carry out an experiment.
First: reserve the disks
Since we want to reserve disks only in a first time, we use the noop job type: with this noop job type, OAR will not try to execute anything on the job resources (which is what we want since disk resources are not capable of executing programs).
(Please mind that Jobs of type noop cannot be interactive:
-I -t noop ... is not supported.)
Reserve two disks on grimoire-1 for one week, starting on 2018-01-01:
Or reserve the first two disks on grimoire-2:
Or reserve all disks on two nodes:
Second: reserve the nodes
In the following example, remove the
You can then reserve nodes grimoire-1 and grimoire-2 for 3 hours, in the usual way:
You must respect this order : reserve the disks first, then reserve the nodes. Otherwise the disks you reserved will not be available on your nodes.
Show and use my reserved disks
Gantt diagrams with disk reservations
Reservations of both nodes (processors) and disks are displayed on the following Gantt diagrams:
Getting information about disk reservations from OAR and G5K APIs
- The OAR API shows the properties of each resource of a job. You can retrieve the properties of your reserved disks, such as disk or diskpath:
- The Grid'5000 API also provide some details about disk reservations under the "disks" key of the status and jobs APIs:
Show disks once connected on the machines
Once connected to a node where you reserved one or more disks, several tools can be used to manage the disk(s):
lsblkwill show you the block devices of your disks: sdb, sdc, ... (be careful: sda is the system disk);
- Commands like
partedcan be used to partition the disk, if needed;
mkfscan be used to format the disk.
Mind that the platform provides access to the block devices. It does not manage partitioning nor formatting nor mounting.
The mechanism used to enable/disable disks is designed to avoid mistakes from other users. However, a malicious user could take control of the RAID card, enable any disk, and access or erase your data. Please notify the Grid'5000 tech-team in case of such event, but first of all mind securing your data:
- Keep a copy (backup) in a safe place if relevant for your data ;
- If your data is sensitive, mind using cryptographic mechanisms to secure it.
Also, the data on reserved disks is not automatically erased at the end of your job. If you don't want the next user to access it, you have to erase it yourself.
Finally, no backup of data stored on the reserved disks is made.