Hub/Switch Installation Guide

Chapter 3 System Preparation
198 September 2002 HPSS Installation Guide
Release 4.5, Revision 2
❖ StorageClassSharing-Areany storageclassessharedamongst morethanone
hierarchy?Ifso,is thatintentionaland ifso,discuss ramificationofsharing vs.
notsharing(usuallyboilsdowntoavoiding“pockets”ofunusedstorage– one
SC full while another is nearly empty – vs. not being able to separate one set
of users or accesses from another).
➢ Disk Storage Class List
❖ Minimum & Maximum Storage Segment Sizes / Average Number of
Segments-Verify that thevaluesspecified, reasonablybalancethe trade-offof
causingHPSStotrack toomany segments (segmentsizestoo smallor average
number of segmentstoo large)vs. wasting too muchspaceon average perfile
(segment sizes too large or average number of segments too small). If a good
value can not be found for the expected file size distribution to balance these
two extremes, maybe we need more storage classes?
❖ Virtual VolumeBlock Size&StripeWidth- Whenstripingisused, you needto
be alittlecareful that thesevaluesfitwell withthose ofany other storage class
which is in thesamehierarchy,aswewillpotentiallybemoving databetween
the levels and need to be sure that when the two sets of Movers are chatting
thatwe don’twindup withexcessive overhead,nordowe windup withextra
tape segments.
A general ruleofthumbistohave theVirtual Volume BlockSizevaluesbethe
same,sothatwithgoodpowerof twostripewidths,wewind upwith adecent
setofMoverto Moverconnections (i.e., eachMoveron oneside does nothave
to connect toeveryMoverontheother).This alsousually guaranteesthatyou
don’t wind up with more than one Mover on one side waiting for one on the
other.
The other consideration is to be sure that the minimum disk storage segment
sizetimes32 (thisisthe maximumnumberof source/sinkdescriptorsperIOD
–ifthismaximumchanges,pleasechangethese guidelines)isa multipleofthe
tape Virtual Volume Block Size times the stripe width. If this is not true, we
could wind up with extra tape storage segments for a file due to the fact that
the disk side can only send 32 segments in an IOD.
❖ Thresholds- Verify that the threshold values seem reasonable. Compare them
to the thresholds for the purge policy – will the SC thresholds be reached
beforepurging is kicked off?If so,then atleast thewarning levelwill likelybe
ignored after a period of time.
❖ Migration & PurgePolicy Ids-Onethingtoconsiderishowmanytapedrives
willbeallocated shouldmorethan oneof these storageclassesbe migratingat
once. If a large percentage of the drives – or even more drives than are
physically available – are reserved for migration at a given point in time, will
the retrieval response be acceptable?
➢ Tape Storage Class List
❖ Media block size
❖ Blocks Between Tape Marks - Verify that these two match the admin guide
(which should actually be the default values for 4.2). If not, why not?