Speaker
Prof.
Manuel Delfino Reznicek
(Port d'Informació Científica (PIC))
Description
Small files pose performance issues for Mass Storage Systems, particularly those
using magnetic tape. The ViVo project reported at CHEP06 solved some of these
problems by using Virtual Volumes based on ISO images containing the small files, and
only storing and retrieving these images from the MSS. Retrieval was handled using
Unix automounters, requiring deployment of ISO servers with a separately managed
cache. We report developments which extend the use of ISO-based Virtual Volumes to
the dCache storage management system, using Castor1 or ENSTORE as the tape back-end.
By using the MSS interface already implemented and documented in dCache, we have been
able to catalog files into dCache, pack them into ISO volumes, store the ISO images
to tape and then transparently allow retrieval of the individual files by dCache. A
simple catalog of files and corresponding ISO images allows us to fetch from tape the
precise ISO image containing the requested file when it is requested by the dCache
MSS interface. We also have developed a cache read-ahead technique that allows the
injection of all files in an ISO image from MSS into dCache, triggered by an original
single file request at the user level. This can provide a high tape efficiency if the
files in each ISO image have been chosen to have a high probability of being
requested within a short period of time. This also allows delegation back to dCache
of most of the ISO-related (or Virtual Volume related) cache management, simplifying
implementation and maintenance.
Primary author
Prof.
Manuel Delfino Reznicek
(Port d'Informació Científica (PIC))
Co-authors
Mr
Daniel Alvarez
(Universitat Autònoma de Barcelona)
Ms
Esther Acción
(Port d'Informació Científica (PIC))
Prof.
Miquel-Angel Senar
(Universitat Autònoma de Barcelona)
