# Accessing HPSS¶

You can access NERSC's HPSS in a variety of different ways. HSI and HTAR are the best ways to transfer data in and out of HPSS within NERSC. Globus is recommended for transfers to or from outside NERSC. We also offer access via gridFTP, pftp, and ftp.

Users are limited to 15 concurrent sessions. This number can be temporarily reduced if a user is impacting system usability for others.

## Automatic Token Generation for use at NERSC¶

The first time you try to connect from a NERSC system (Cori, DTNs, etc.) using a NERSC provided client like HSI, HTAR, or pftp you will be prompted for your NIM password + one-time password which will generate a token stored in $HOME/.netrc. After completing this step you will be able to connect to HPSS without typing a password: hsi Generating .netrc entry... elvis@auth2.nersc.gov's password:  If you have an existing$HOME/.netrc file and you are having problems connecting to either HPSS system try moving this file to temp.netrc and re-connect to HPSS. If the problem persists contact NERSC account support.

## HSI¶

HSI is a flexible and powerful command-line utility to access the NERSC HPSS storage systems. You can use it to store and retrieve files and it has a large set of commands for listing your files and directories, creating directories, changing file permissions, etc. The command set has a UNIX look and feel (e.g. mv, mkdir, rm, cp, cd, etc.) so that moving through your HPSS directory tree is close to what you would find on a UNIX file system. HSI can be used both interactively or in batch scripts.

The HSI utility is available on all NERSC production computer systems and it has been configured on these systems to use high-bandwidth parallel transfers.

### HSI Usage Examples¶

All of the NERSC computational systems available to users have the hsi client already installed. To access the Archive storage system you can type hsi with no arguments. This will put you in an interactive command shell, placing you in your home directory on the Archive system. From this shell, you can run the ls command to see your files, cd into storage system subdirectories, put files into the storage system and get files from it.

In addition to command line, you can run hsi commands several different ways:

• Single-line execution: hsi "mkdir run123; cd run123; put bigdata.0311
• Read commands from a file: hsi "in command_file"
• Read commands from standard input: hsi < command_file
• Read commands from a pipe: cat command_file | hsi

The hsi utility uses a special syntax to specify local and HPSS file names when using the put and get commands. The local file name is always on the left and the HPSS file name is always on the right and a ":" (colon character) is used to separate the names

There are some shortcuts, for instance the command put myfile.txt will store the file named "myfile" from your current local file system directory into a file of the same name into your current HPSS directory. If you wanted to put it into a specific HPSS directory, you can also do something like hsi "cd run123; put myfile.txt"

Most of the standard Linux commands work in hsi (cd, ls,rm,chmod,etc.). There are a few commands that are unique to hsi

Command Function
get, mget Copy one or more HPSS-resident files to local files
cget Conditional get - get the file only if it doesn't already exist on the target
put, mput Copy one or more local files to HPSS
cput Conditional put - copy the file into HPSS unless it is already there

Hsi also has a series of "local" commands, that act on the non-HPSS side of things:

Command Function
lcd Change local directory
lls List local directory
lmkdir Make a local directory
lpwd Print current local directory
command Issue shell command

#### Removing Older Files¶

You can find and remove older files in HPSS using the hsi find command. This may be useful if you're doing periodic backups of directories (this is not recommended for software version control, instead use a versioning system like git) and want to delete older backups. Since you can't use a linux pipe ("|") in hsi, you need a multi-step process. The example below will find files older than 10 days and delete them from HPSS.

hsi -q "find . -ctime 10" > temp.txt 2>&1
cat temp.txt | awk '{print "rm -R",\$0}' > temp1.txt
hsi in temp1.txt


#### Removing Entire Directories¶

To recursively remove a directory and all of its contained sub-directories and files, use rm -R <directory_name>.

## HTAR¶

HTAR is a command line utility that creates and manipulates HPSS-resident tar-format archive files. It is ideal for storing groups of files in HPSS. Since the tar file is created directly in HPSS, it is generally faster and uses less local space than creating a local tar file then storing that into HPSS. HTAR also does inline compression so compressing the data befrehand is unnecessary. Furthermore, HTAR creates an index file that (by default) is stored along with the archive in HPSS. This allows you to list the contents of an archive without retrieving it from tape first. The index file is only created if the HTAR bundle is successfully stored in the archive.

HTAR is installed and maintained on all NERSC production systems. If you need to access the member files of an HTAR archive from a system that does not have the HTAR utility installed, you can retrieve the tar file to a local file system and extract the member files using the local tar utility.

HTAR is useful for storing groups of related files that you will probably want to access as a group in the future. Examples include:

• archiving a source code directory tree
• archiving output files from a code simulation run
• archiving files generated by an experimental run

If stored individually, the files will likely be distributed across a collection of tapes, requiring long delays (due to multiple tape mounts) when fetching them from HPSS. On the other hand, an HTAR archive file will likely be stored on a single tape, requiring only a single tape mount when it comes time to retrieve the data.

The basic syntax of HTAR is similar to the standard tar utility:

htar -{c|K|t|x|X} -f tarfile [directories] [files]

As with the standard unix tar utility the "-c" "-x" and "-t" options respectively function to create, extract, and list tar archive files. The "-K" option verifies an existing tarfile in HPSS and the "-X" option can be used to re-create the index file for an existing archive.

Please note, you cannot add or append files to an existing archive.

When HTAR creates an archive, it places an additional file (with an idx postfix) at the end of the archive. This is an index file that HTAR can use to more quickly retrieve individual files from your bundle. It is only created if the htar completed successfully.

If your htar files are 100 GBs or larger and you only want to extract one or two small member files, you may find faster retrieval rates by skipping staging the file to the HPSS disk cache by adding the "-Hnostage" option to your htar command.

### HTAR tips¶

• Using htar to backup directories obviates the need to tar the directories locally first
• htar compresses data inline, so you don't need to gzip it
• Try to only bundle 100GB-500GB in any single htar call
• If you have a truly huge amount of data to archive, try not to archive more than 100TB per day. This will help in allowing others to use the archive at the same time
• To retrieve only a few members from a large htar archive, use the -Hnostage option to avoid untarring the whole file into the staging area

### HTAR Usage Examples¶

Create an archive with directory "nova" and file "simulator"

htar -cvf nova.tar nova simulator
HTAR: a   nova/
HTAR: a   nova/sn1987a
HTAR: a   nova/sn1993j
HTAR: a   nova/sn2005e
HTAR: a   simulator
HTAR: a   /scratch/scratchdirs/elvis/HTAR_CF_CHK_61406_1285375012
HTAR Create complete for nova.tar. 28,396,544 bytes written for 4 member files, max threads: 4 Transfer time: 0.420 seconds (67.534 MB/s)
HTAR: HTAR SUCCESSFUL


Now list the contents:

htar -tf nova.tar
HTAR: drwx------  elvis/elvis          0 2010-09-24 14:24  nova/
HTAR: -rwx------  elvis/elvis    9331200 2010-09-24 14:24  nova/sn1987a
HTAR: -rwx------  elvis/elvis    9331200 2010-09-24 14:24  nova/sn1993j
HTAR: -rwx------  elvis/elvis    9331200 2010-09-24 14:24  nova/sn2005e
HTAR: -rwx------  elvis/elvis     398552 2010-09-24 17:35  simulator
HTAR: -rw-------  elvis/elvis        256 2010-09-24 17:36  /scratch/scratchdirs/elvis/HTAR_CF_CHK_61406_1285375012
HTAR: HTAR SUCCESSFUL


As an example, using hsi remove the nova.tar.idx index file from HPSS (Note: you generally do not want to do this)

hsi "rm nova.tar.idx"
rm: /home/j/elvis/nova.tar.idx (2010/09/24 17:36:53 3360 bytes)


Now try to list the archive contents without the index file:

htar -tf nova.tar
ERROR: No such file: nova.tar.idx
ERROR: Fatal error opening index file: nova.tar.idx
HTAR: HTAR FAILED


Here is how we can rebuild the index file if it is accidently deleted

htar -Xvf nova.tar
HTAR: i nova
HTAR: i nova/sn1987a
HTAR: i nova/sn1993j
HTAR: i nova/sn2005e
HTAR: i simulator
HTAR: i /scratch/scratchdirs/elvis/HTAR_CF_CHK_61406_1285375012
HTAR: Build Index complete for nova.tar, 5 files 6 total objects, size=28,396,544 bytes
HTAR: HTAR SUCCESSFUL

htar -tf nova.tar
HTAR: drwx------  elvis/elvis          0 2010-09-24 14:24  nova/
HTAR: -rwx------  elvis/elvis    9331200 2010-09-24 14:24  nova/sn1987a
HTAR: -rwx------  elvis/elvis    9331200 2010-09-24 14:24  nova/sn1993j
HTAR: -rwx------  elvis/elvis    9331200 2010-09-24 14:24  nova/sn2005e
HTAR: -rwx------  elvis/elvis     398552 2010-09-24 17:35  simulator
HTAR: -rw-------  elvis/elvis    256 2010-09-24 17:36  /scratch/scratchdirs/elvis/HTAR_CF_CHK_61406_1285375012
HTAR: HTAR SUCCESSFUL


Here is how we extract a single file from a htar file

htar -xvf nova.tar simulator

#### Using ListFiles to Create an HTAR Archive¶

Rather than specifying the list of files and directories on the command line when creating an HTAR archive, you can place the list of file and directory pathnames into a ListFile and use the "-L" option. The contents of the ListFile must contain exactly one pathname per line.

find nova -name 'sn19*' -print > novalist

cat novalist
nova/sn1987a
nova/sn1993j


Now create an archive containing only these files

htar -cvf nova19.tar -L novalist
HTAR: a   nova/sn1987a
HTAR: a   nova/sn1993j

htar -tf nova19.tar
HTAR: -rwx------  elvis/elvis    9331200 2010-09-24 14:24  nova/sn1987a
HTAR: -rwx------  elvis/elvis    9331200 2010-09-24 14:24  nova/sn1993j


#### Soft Delete and Undelete¶

The "-D" option can be used to "soft delete" one or more member files or directories from an HTAR archive. The files are not really deleted, but simply marked in the index file as deleted. A file that is soft-deleted will not be retrieved from the archive during an extract operation. If you list the contents of the archive, soft deleted files will have a 'D' character after the mode bits in the listing:

htar -Df nova.tar nova/sn1993j
HTAR: d  nova/sn1993j
HTAR: HTAR SUCCESSFUL


Now list the files and note that sn1993j is marked as deleted:

htar -tf nova.tar
HTAR: drwx------   elvis/elvis          0 2010-09-24 14:24  nova/
HTAR: -rwx------   elvis/elvis    9331200 2010-09-24 14:24  nova/sn1987a
HTAR: -rwx------ D elvis/elvis    9331200 2010-09-24 14:24  nova/sn1993j
HTAR: -rwx------   elvis/elvis    9331200 2010-09-24 14:24  nova/sn2005e

To undelete the file, use the -U option:

htar -Uf nova.tar nova/sn1993j
HTAR: u  nova/sn1993j
HTAR: HTAR SUCCESSFUL


List the file and note that the 'D' is missing

htar -tf nova.tar nova/sn1993j
HTAR: -rwx------  elvis/elvis    9331200 2010-09-24 14:24  nova/sn1993j


### HTAR Archive Verification¶

You can request that HTAR compute and save checksum values for each member file during archive creation. The checksums are saved in the corresponding HTAR index file. You can then further request that HTAR compute checksums of the files as you extract them from the archive and compare the values to what it has stored in the index file.

htar -Hcrc -cvf nova.tar nova
HTAR: a   nova/
HTAR: a   nova/sn1987a
HTAR: a   nova/sn1993j
HTAR: a   nova/sn2005e


Now, in another directory, extract the files and request verification

htar -Hverify=crc -xvf nova.tar
HTAR: x nova/
HTAR: x nova/sn1987a, 9331200 bytes, 18226 media blocks
HTAR: x nova/sn1993j, 9331200 bytes, 18226 media blocks


### HTAR Limitations¶

HTAR has several limitations to be aware of:

#### Member File Path Length¶

File path names within an HTAR aggregate of the form prefix/name are limited to 154 characters for the prefix and 99 characters for the file name. Link names cannot exceed 99 characters.

#### Member File Size¶

The maximum file size the NERSC archive will support is approximately 20 TB. However, we recommend you aim for HTAR aggregate sizes of several hundred GBs. Member files within an HTAR aggregate are limited to approximately 68GB.

#### Member File Limit¶

HTAR aggregates have a default soft limit of 1,000,000 (1 million) member files. Users can increase this limit to a maximum hard limit of 5,000,000 member file.

## Globus¶

Globus is recommended for transfers between sites (i.e. non-NERSC to NERSC).

To access the HPSS system using Globus, you first need to create a Globus account. Once you've created an account you can log in either with your Globus information or with your NERSC account information. The first time you log in using your NERSC account you'll be asked to enter your Globus account information as well.

The NERSC HPSS endpoint is called "NERSC HPSS". You can use the GUI to transfer files. Currently, there is no explicit ordering by tape of file retrievals for Globus. If you're retrieving a large data set with Globus, we recommend that users see this page for instructions on how to best order files using HSI and then retrieve files using the command line interace for Globus in tape order.

## GridFTP, pftp, and ftp¶

Files can be transferred between HPSS and remote sites via the standard internet protocol ftp, however, being non-parallel the performance of ftp will probably not be as good as other methods such as gridFTP. Note that on NERSC systems ftp translates to pftp so it is in fact parallel. There is no sftp (secure ftp) or scp access.

As standard ftp clients only support authentication via the transmission of unencrypted passwords, which NERSC does not permit, special procedures must be used with ftp on remote sites, see HPSS Passwords.

The HPSS systems use NIM and the NERSC LDAP server to create an "hpss token" for user authentication. The HPSS token does not expire and users may generate new tokens as often as they wish and old tokens will still be honored. If a user wishes to disable previously generated tokens for security reasons contact the NERSC help desk.

Because HPSS passwords do not expire it is only necessary to generate a password one time for continued use of HPSS. This password is placed in a file name ".netrc" for use by hsi, htar, pftp, and most ftp clients.