Storage Services Adminstration (SSA) Group

dCache


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Overview

dCache is a data caching software/hardware system that is positioned between the user and a Hierarchial Storage Manager (Enstore). dCache is a collaboration between Fermilab and DESY. Desy maintains the core dcache functionality and Fermilab writes access doors, monitoring etc. The dCache software runs on a set of dedicated hosts. These dedicated hosts consist of a Pool Manager ( xxxendca3a ) and the space pools ( xxxendca4a, 5a etc. or the pool can be on xxxendca3a if it is a one host system. The Pool is a host or hosts that have a lot of disk space. This used for the cache. dCache interfaces with PNFS on the Enstore system's PNFS server (xxxensrv1). The dCache PNFS Manager runs there.


HSM ( Enstore )goals realized by using dCache are:


  1. Minimized mount and dismount operations,
  2. Predictable data rates (streaming Tapes).
  3. Use of slow tape and robot devices.

Client (user) Benefits:


  1. Random Repository Access
  2. Random File Access
  3. Arbitrary Transfer Rate
  4. It is possible to read part of a file and not transfer the entire file (posix IO).

Data Transfer Methods to/from the dcache:

  1. dccp: dCache cp. This binary can be found in the dcap product in KITS. It can be used in 2 ways: with pnfs mounted on a client node, and without pnfs mounted if the user allows other read access on their files.
  2. Weak ftp reads. You can use any ftp client. Passwords are stored in the dcache.pwd file on the admin node's config directory.
  3. Kerberized ftp read/write. You can use any kerberized ftp client. We provide kftp, which is in the kftp product in KITS. Allowed principles are stored in the dcache.kpwd file in the admin node's config directory.
  4. Globus-url-copy (aka gridftp). Right now the only credentials we allow the the x509 certs from the fermilab kca. This means you also need a kerberos ticket. [This is only because this is what FNAL policy requires.]

dCache Components:

  1. An admin node - we are responsible for everything on these nodes. The current admin nodes are:

  2. Write pools. These are node that, once a file is copied there by a user, we 'guarantee' the files are as good as on tape. We are responsible for everything on these write pool nodes. The current write pools are:

  3. Read Pools: We are responsible for everything on these read pools:

Software is always installed at ~enstore/dcache-deploy

More information about dCache can be found at http://stkensrv2.fnal.gov/enstore/dcache.html and www-dcache.desy.de

Related Pages

  1. dCache User Administration (Information on this page Is not accurate)
  2. Starting and Stopping dCache
  3. Monitoring dCache
  4. Current dCache Hardware Configurations
  5. pageDcache failure on CDFendca3



The URL for this page is http://www-isd.fnal.gov/ISA/dCache.html
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ssa-group@fnal.gov