Filesystems available under Unix

There are several filesystems available. The table below summarizes most of them.

Filesystem	Purpose	How to access	Notes	Backups
/usa	Home directories	/usa/$USER	ZFS, available with NFS, SMB and AFP	ZFS snapshots remote replication
/usb	Web directories	/usb/$USER/public_html	ZFS, web-accessible, available on PCs	ZFS snapshots remote replication
/NODENAME	Local disks	cd /NODENAME	replace NODENAME with hostname minus domain. No quotas	ZFS snapshots remote replication or none

These all have quotas except for the /NODENAME disks. The /NODENAME disks are available on other hosts through NFS as /m/NODENAME. Just cd /m/NODENAME to access one.

Available disk space can be seen by using the dfcommand. For example df -h . for info on the filesystem you are currently in or df -h /m/NODENAME, etc.

Quota policy

The current quota policy on the main research network for home directories is 25GB limit for undergrads, 50GB limit for graduate students (Staff, Professionals, etc.) and 100GB for faculty. The mail spool also has a quota (1GB, 2GB and 4GB respectively for undergrads, grads and faculty). Home directories are found under /usa/$USER. Additional space is available (intended for web usage) on the main research network under /usb/$USER. This space also has a quota, that varies according to the users’ status.

Note: Research home directories were upgraded to larger quotas with ZFS in Summer 2009.

To list your current quota on any filesystem use ‘df -h .’ while in that filesystem. Your limit will be listed under size and what you are using and have available will also be listed. All core ECE/CIS systems are using ZFS.

For ZFS filesystems the quota command does not apply. The df command must be used instead. Also read below about ZFS for more info. In the case of samba filesystems Windows will also report the amount of space used and available.

ZFS info

ZFS is a new file system from Sun that has some revolutionary features. Most of those features are of interest to admins and those interested in filesystem research.

Quotas

With ZFS, instead of having many users per filesystem and having quotas based on the user ID, each user has their own filesystem. The quota command does NOT apply to ZFS filesystems. Instead, the df command should be used to see how much space is available. Please pay attention to your space free. Also, read below for how snapshots affect disk space usage.

If you run into quota exceeded messages you can truncate a large file by redirecting /dev/null to the file, and afterwards you should be able to remove it as normal. ex: cat /dev/null >! ~/bigfile. If this does not work start a bash shell and try the command :>! ~/bigfile which should set the file to zero length.

There are other solutions as well, please read the section on Snapshots before posting a help request.

Snapshots

ZFS supports snapshots, which are read-only images of the filesystem at the time the snapshot is taken. They are available under the .zfs/snapshot directory from the base of the filesystem (every user has their own ZFS filesystems). For example, for your home directory look in /usa/$USER/.zfs/snapshot. The .zfs directory may not show up in a directory listing using ls -a as it is hidden, but changing to it is possible. In there you will find directories with the name of 12, 18, Mon, Tue … Sat, Sun. The 12 snapshot is taken during the noon hour, and the 18 snapshot is taken during the 6pm hour. They are named like this to allow future hourly snapshots to be possibly included. There are also snapshots for each day of the week which are taken during the 11pm hour. Each day during the noon hour the snapshot from the previous day is destroyed and a new one is taken. The same is done during the 6pm hour. During the 11pm hour the snapshot from one week ago is destroyed and a new one is created. When a snapshot is taken no additional space is required. However, as the filesystem changes, copy-on-write is done and will cause snapshots to use space which will be counted toward your quota.

When a snapshot is taken no space is initially used by it as it is a read-only reference for the current filesystem image. As the actual filesystem is changed new blocks are allocated and are counted toward the quota use. Users cannot delete individual files from a snapshot. When a file is removed, that made it to the 11pm snapshot, it does not free space up until one week later.

If you are close to your quota and reach the limit you will receive disk quota exceeded or filesystem full errors. While you can not delete individual files from your snapshots you can now delete the snapshot on ACAD and Research systems using the rmdir command. Ex: rmdir ~/.zfs/snapshot/Mon would delete your Monday snapshot and free up any space used by it.

Special note for Windows users of samba filesystems:

• It has been observed that Windows may think it is deleting files from a snapshot, but the file is actually not removed.
• Windows will show how much space is available in your filesystem.

Some example uses of snapshots for users are:

• If a file is deleted or changed during the afternoon you can go to the 12 noon snapshot and retrieve the file.
• If a file was deleted on Friday and you do not realize until Monday you can use the Thu snapshot to retrieve the file.
• The 6pm snapshot can be used similarly and is also used for nightly backups to backup servers.

Reliability

ZFS uses checksums so data reliability from disk is guaranteed. These filesystem are also resilient to single disk failures, as we configure them (uses raidz which is an improvement of raid5 or raidz2 which is raid6 like). When a disk fails (or is failing) we are notified and it can then be replaced with users not noticing.

Recovering deleted files from snapshots

If a file is deleted, or you need an older version of a file it is possible that it can be retrieved from a backup. First, if the filesystem the file resided in uses ZFS look in .zfs/snapshot.

Remember, your file must have existed when the snapshot was created in order to be restored. If you create a file and delete it five minutes later, it most likely will not be recoverable.

Preventing inadvertent file removal

In order to protect yourself from inadvertently removing files you may wish to look into the following:

• alias rm to rm -i
• alias mv to mv -i

Another thing to consider, if you don’t want to alias rm, is to look into the tcsh rmstar feature. set rmstar will cause tcsh to prompt «Do you really want to delete all files? [n/y]», before removing all files. But be warned that this only works if rm is not aliased, exactly rm * is done and with tcsh not csh.

Access Control Lists (ACLs)

Solaris implements ACLs (Access Control Lists), which give users much more flexibility to share files, than what the standard UNIX permissions offer. ACLs of a UFS file can be viewed with the getfacl command. UFS ACLs are set and manipulated with the setfacl command. On ZFS filesystems, ACLs are viewed with ls -v, and set and manipulated with chmod A.... The man pages of these commands explain the details.

Please continue to the ACLs page for more information and examples of using ACLs.

Using Samba server from PC

Unix home filesystems are available through the samba server, smb1. Once authenticated \\smb1.eecis.udel.edu\username for research homes and \\smb1.acad.ece.udel.edu\username for acad can be mounted on PCs. For more info please see the ECE/CIS SAMBA Mini-Howto.

Also, the research /usb filesystem (for web pages) is available through samba using the \\smb-www.eecis.udel.edu\username.

Using the AFP Server from OS X

The home filesystems are also available over AFP. To see how to connect see AFP.

Backups

For more information, see our backups page.