Difference between revisions of "Disk space"

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== Storage Policy ==
== Storage Policy ==
=== Backups ===
=== Backups ===
3It is important to understand that '''none''' of our main file systems are backed up on other devices. This means that in case of a hardware crash data will be lost.  
It is important to understand that '''none''' of our main file systems are backed up on other devices. This means that in case of a hardware crash data will be lost.
=== Snapshots ===
=== Snapshots ===

Revision as of 12:27, 15 October 2018

Storage Policy


It is important to understand that none of our main file systems are backed up on other devices. This means that in case of a hardware crash data will be lost.


Some file systems, have snapshots, which allow a rollback of the file system to a certain point in time. Snapshots reside on the same file system as the data itself, and, while CSE storage systems have raid protection that guards against single disk failure, without backup, data will be lost if a multiple disk/shelf crash occurs.

The main storage systems are:

Home directories: These directories (/cs/usr/login accessible as "~") reside on a highly capable file server with provided snapshots and 
have the lowest chance of crashing but are relatively more limited in space.
Secondary directories: These directories (/cs/+/usr/login accessible as ~/safe in newer accounts and as ~/.+ in older accounts) generally have more frequent snapshots than the home directories, but usually have a smaller space allocation than the home directories.
Storage for labs:  These are directories that reside under /cs/labs. They provide snapshots
and are the volume of choice for large amounts of data.  Some labs have directories under /cs/snapless which are desired for large volume volatile data and, hence, contain no snapshots.  Lab users that intend to run heavy IO intensive jobs should consult with the CSE System Group first.

Lab storage limits

Each faculty member is allocated up to 2 terabytes of space, which should cover most users. Anyone requiring more space will be asked to pay a yearly amount that will cover the price of additional storage resources. It is important to note that for each terabyte of data 500 gigabyte is reserved for snapshots.

Other filesystems can have varying snapshot policies. Contact the CSE System Group if you want to better understand their status.

Additional recommendations

To safely store code, we suggest using our Github. The github virtual machine and data are backed up on two different file-systems, providing high-level resilience.

Another easy backup option is using the unlimited space Google provides along with your mail HUJI account. Some students and faculty members are using this option and are pleased with the results. Please note that these backups are solely the responsibility of the user and are in no way supported by the CSE System Group.

Snapshots do not behave well with heavy writes. If your lab needs to write a lot of data or do heavy reads please contact us for further assistance.

Disk Quotas

Users are allocated disk quota as follows:

File System Type
Account typeGroupHomeSecondary
visting lecturervisitor5G1G
external graduatecgrad2G2G
external phdcphd4G4G

To see how much quota you have, type nquota. Note that the data for nquota is updated once every few minutes.


Snapshots are short-term online backups. There are three types of snapshots: hourly, daily and weekly. Snapshots cycle out -- i.e. if N hourly snapshots are defined for a filesystem, when the next snapshot is created, the oldest ([N+1) snapshot disappears permanently. Note that online means that the snapshots are part of the filesystem. If a filesystem becomes unavailable due to a fileserver failure, the snapshots are unavailable as well.

In home and secondary directories, snapshots are available in the special .snapshot directory and can be accessed using the snapshot utility or directly (e.g. "cd .snapshot"). Note that the .snapshot doesn't show up when searching a directory (i.e. "ls -a" won't show it), but it exists and can be "cd"-ed into.

In graduate lab directories, the snapshots appear under /cs/labs/supervisor/.zfs/snapshot where supervisor is the login of the faculty member under whom the graduate student is doing his graduate degree, The nature of these snapshots are explained in the section on ZFS filesystems.

The current snapshot schedule is as follows:

File System TypePathHourlyDailyWeekly
Secondary~/safe or ~/.+24148
Graduate Labs/cs/labs/supervisor/login2474

ZFS Filesystems

Lab filesystems (in particular, /cs/labs) are stored in ZFS filesystems.

ZFS filesystems differ from home and secondary directories by the fact that, with ZFS, snapshots are a hidden part of the filesystem and, as such, the filesystem will appear to shrink in Linux df outputs.

For example, a new ZFS filesystem called '/cs/zogmir is created with a 1 TB space allocation and snapshots enabled:

% df -h /cs/zogmir
Filesystem               Size  Used Avail Use% Mounted on
zfs-server:/h/zogmir       1T   19k    1T   0% /cs/zogmir

With time, users save and delete large files so snapshots take up 179 GB and the filesystem appears to shrink:

% df -h /cs/zogmir
Filesystem               Size  Used Avail Use% Mounted on
zfs-server:/h/zogmir     821G  305G  516G  37% /cs/zogmir

And yet further use, causes the snapshots to take up more than a third of the filesystem (356 GB):

% df -h /cs/zogmir
Filesystem               Size  Used Avail Use% Mounted on
zfs-server:/h/zogmir     644G  483G  161G  75% /cs/zogmir

At this point of time, there is no way to see on Linux how much of a ZFS filesystem is taken up by snapshots so when a filesystem shrinks to show a capacity of more than 95%, the CSE System Group should be contacted since, once the filesystem is 100%, it is impossible to erase files since any erasure attempt tries to put erased blocks in the snapshots that reside in the same filesystem.

Disk space shortage

Logging in without quota

If there is insufficient disk space, some window managers might not start at all. When this happens you'll receive some message of insufficient quota, or an error message saying the Xsession has terminated too quickly. In this case, to be able to login and clean up your quota, you'll have to login using xterm.

There are two ways to login in xterm:

  1. When the chooser appears, choose XTerm instead of the normal window manager you use.
  2. Before logging in (i.e. entering the username and password), click on the Session button, and choose Failsafe Terminal

After you've logged in, you'll get a simple xterm window. There you can start cleaning up your quota as described in the following sections. When finished, simply type exit, and re-login again.

Note: Without a window manager, to write commands to the xterm window, you'll have to place the mouse courser on that window.

Basic cleanup

Some basic utilities to manage disk space:

  1. Are you using your secondary storage area (~/safe or ~/.+)?
    If not there's more space there you can use.
  2. Use the cleanup script to remove files that can be safely deleted:
  3. Use du to find how space is distributed within your home directory:
    du ~ | sort -rn
    Note that this will also show you the space taken by files beginning with '.' which do not normally show in directory listings.
    A more elaborate usage of the du utility is:
    \ls -A1 | sed "s#'#\\\'#" | sed 's/ /\\ /g' | xargs du -sckx -- | sort -n
    Which will calculate the sum of each directory (in the current directory).
  4. Graduate students can avoid creating large dot directories by installing software in their /cs/labs directory using virtual environment -- e.g.
    virtualenv /cs/labs/einstein/shainde/venv-01

Other Tips for freeing some disk space

  • Compress directories and files that aren't used regularly, using the command:
     tar cvzf <archive file> <list of files>
    and remove these files
    rm <list of files>
    or in one command
    tar --remove-files cvfz <archive file> <list of files>
    If you want to decompress those files, use the command:
    tar xvzf <archive file>
  • If you want to view the disk-space used by a specific directory (and its descendants) type:
     du -sh <directory>
  • Free space in your home directory by moving something to secondary storage. For example to move your firefox configuration, do:
mv ~/.mozilla ~/.+
ln -s .+/.mozilla ~
  • Graduate students should move large dot directories to their lab storage -- i.e.
mv ~/.cache ~/.config ~/.local ~/.ntprofile.V2  /cs/labs/supervisor/login/
ln -s /cs/labs/supervisor/login/.cache ~
ln -s /cs/labs/supervisor/login/.config ~
ln -s /cs/labs/supervisor/login/.local ~
ln -s /cs/labs/supervisor/login/.ntprofile.V2 ~