Hub/Switch Installation Guide

Chapter 2 HPSS Planning
HPSS Installation Guide September 2002 97
Release 4.5, Revision 2
Explanation: The Class of Service (COS) mechanism can be used to place files in the appropriate
place. Notethat although theBitfile Server provides the abilityto use COSselection, currentHPSS
interfacesonlytake advantageof this intwocases. First,the pput commandinPFTP automatically
takes advantage of this by selecting a COS based on the size of the file. If the FTP implementation
on the client side supports the alloc command, a COS can also be selected based on file size. Files
can also be directed to a particular COS with FTP and PFTP commands by using the site setcos
command to select a COS before the files are stored. When setting up Classes of Service for disk
hierarchies,take into account boththe Storage Segment Size parameterandthe Maximum Storage
SegmentSize parameterin determiningwhatrangeoffilesizesaparticularCOSwillbe configured
for.
NFS is more of a challenge in this area. NFS puts all the files it creates into a particular class of
service, independent of the file size. If a fileset has a class of service associated with it, files will be
put into thatclass of service. Otherwise, thedaemon’s class of service willbe used. Sites may want
tosetup differentfilesetstodealwithlargeandsmall files,andassignaclassofserviceaccordingly.
It is important to use the Storage Segment Size, Maximum Storage Segment Size, and Average
Numberof Segmentsparametersto allowforthe rangeof filesizesthat clientstypically storein the
fileset. Remember that NFS V2 files cannot be larger than 2GB.
2.9.1.7 Maximum Storage Size Selection (disk only)
This parameter, along with Storage Segment Size and Average Number of Storage Segments, is
usedbythe BitfileServerto optimallychooseastorage segment sizefor bitfilesondisk.The largest
storage segment size that can be selected for a file in a storage class is limited by this parameter.
Guideline: In order to avoid creating excessive fragmentation of the space on disks in this storage
class,itis recommendedthatthis parameterbe set nohigherthat 5%of thesizeof thesmallest disk
allocated to this storage class.
2.9.1.8 Maximum VVs to Write (tape only)
Thisparameterrestrictsthenumber oftapeVVs, per storageclass, thatcanbeconcurrentlywritten
by the Tape Storage Server. The purpose of the parameter is to limit the number of tape VVs being
written toprevent filesfrom beingscattered overa number oftapes and tominimize tape mounts.
The number of tape drives used to write files in the storage class will be limited to approximately
the value of this field times the stripe width defined for the storage class. Note that this field only
affects tape write operations. Read operations are not limited by the value defined by this
parameter.
2.9.1.9 Average Number of Storage Segments (disk only)
This parameter, along with Storage Segment Size and Maximum Storage Segment Size, is used by
the Bitfile Server to optimally choose a storage segment size for bitfiles on disk. The Bitfile Server
attempts to choose a storage segment size between Storage Segment Size and Maximum Storage
Segment Size that would result in creating the number of segments indicated by this parameter.
Guideline: For best results, it is recommended that small values (< 10) be used. This results in
minimizing metadata created and optimizing migration performance. The default of 4 will be
appropriate in most situations.