Disk reservation

From Grid5000
Revision as of 19:27, 19 March 2019 by Pneyron (talk | contribs)

(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search
See also: Storage overview | Storage Manager | Group Storage | Ceph | Local (on nodes) disks reservation
Note.png Note

This tutorial is actively maintained by the Grid'5000 team. If you encounter problems, please report them (see the Support page). Additionally, as it is a wiki page, you are free to make minor corrections yourself if needed. If you would like to suggest a more fundamental change, please contact the Grid'5000 team.

Disk reservation consists in reserving on nodes additional hard disks, which are otherwise not usable.

The table below shows the Grid'5000 clusters with such additional hard disks available for reservation.

Site Cluster Number of nodes Number of reservable disks per node
Grenoble yeti 4 3
Lille chiclet 8 2
Lille chifflet 8 3
Lille chifflot 8 5
Nancy grimoire 8 5
Rennes parasilo 28 5
Last generated from the Grid'5000 Reference API on 2018-11-16 (commit 80754da21)

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 noop OAR 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 deploy OAR job type, then kadeploy)
  • or in a non-deploy job, in the standard environment but after enabling sudo with the sudo-g5k command.

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.

Usage

The main commands to reserve disks are given below.

Note.png Note

Note that accessing the data stored on reserved disks on nodes is only possible with reservation of type deploy (oarsub -t deploy ...). Non-deploy jobs do not give access to disks (only the system disk).

The maximum duration of a disk reservation is defined in the Usage Policy.

Reserve disks and nodes at the same time

Note.png Note

In the 3 following examples, remove the -t deploy if you plan to use the standard environment and sudo-g5k in order to get the root privileges, instead of kadeploy and be root in you own deployed environment.

How to reserve a node with only the main disk (none of the additional disks), on the grimoire cluster
Terminal.png fnancy:
oarsub -I -t deploy -p "cluster='grimoire'" -l /host=1

(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
Terminal.png fnancy:
oarsub -I -t deploy -l {"(type='disk' or type='default') and cluster='grimoire'"}/host=1
How to reserve nodes grimoire-1 and grimoire-2 with one reservable disk per node
Terminal.png fnancy:
oarsub -I -t deploy -p "host in ('grimoire-1.nancy.grid5000.fr','grimoire-2.nancy.grid5000.fr')" -l /host=2+{"type='disk'"}/host=2/disk=1
Note.png Note

Yes, the syntax of the last oarsub command is a bit awkward, so please be careful and mind having:

  • the -p option explicitly set the hosts you want (using "cluster='grimoire'" instead could not insure that you get the disks on the same nodes you will reserve) ;
  • both host= values in the -l option (2 in the example) exactly match the count of hosts in the list you provide in the -p option (grimoire-1.nancy.grid5000.fr and grimoire-2.nancy.grid5000.fr in the example).
  • we do not need to explicitly write "{type='default'}" in the -l option (before the /host=2+, because default is implicit is the type is not set.
See Advanced OAR for more explanation of the oarsub syntax.

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: oarsub-I -t noop ... is not supported.)

3 examples:

Reserve two disks on grimoire-1 for one week, starting on 2018-01-01:

Terminal.png fnancy:
oarsub -r "2018-01-01 00:00:00" -t noop -l {"type='disk' and host='grimoire-1.nancy.grid5000.fr'"}/host=1/disk=2,walltime=168

Or reserve the first two disks on grimoire-2:

Terminal.png fnancy:
oarsub -r "2018-01-01 00:00:00" -t noop -l {"type='disk' and host='grimoire-2.nancy.grid5000.fr' and disk in ('sdb.grimoire-2', 'sdc.grimoire-2')"}/host=1/disk=2,walltime=168

Or reserve all disks on two nodes:

Terminal.png fnancy:
oarsub -r "2018-01-01 00:00:00" -t noop -l {"type='disk' and cluster='grimoire'"}/host=2/disk=ALL,walltime=168

Second: reserve the nodes

Note.png Note

In the following example, remove the -t deploy if you plan to use the standard environment and sudo-g5k in order to get the root privileges, instead of kadeploy and be root in you own deployed environment.

You can then reserve nodes grimoire-1 and grimoire-2 for 3 hours, in the usual way:

Terminal.png fnancy:
oarsub -I -t deploy -l {"host in ('grimoire-1.nancy.grid5000.fr', 'grimoire-2.nancy.grid5000.fr')"}/host=2,walltime=3

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:

Grenoble

Lille

Nancy

Rennes

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:
Terminal.png fnancy:
curl https://api.grid5000.fr/stable/sites/site/internal/oarapi/jobs/job_id/resources.json (or resources.yaml)
  • The Grid'5000 API also provide some details about disk reservations under the "disks" key of the status and jobs APIs:
Terminal.png fnancy:
curl https://api.grid5000.fr/stable/sites/site/status | json_pp
Terminal.png fnancy:
curl https://api.grid5000.fr/stable/sites/site/jobs/job_id | json_pp

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):

  • lsblk will show you the block devices of your disks: sdb, sdc, ... (be careful: sda is the system disk);
  • Commands like fdisk or parted can be used to partition the disk, if needed;
  • mkfs can 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.

Security issues

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.