Service Manuals, User Guides, Schematic Diagrams or docs for : xerox sdd memos_1978 19780615_Scavenger_Copydisk_InitializeDisk
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XEROX SDD ARCHIVES
I have read and understood
Pages _________To _________
)(FRO)( Reviewer Date_ _ __
HUSlNESS SYSTEMS # of Pages_ _R.ef 7g.sJJJ:J -1'-.3
0,
System Development Division
To: Distribution Date: June 15, 1978
From: W. C. Lynch Location: Palo Alto
Subject: Scavenger, Copydisk, Organization: SDD/SD/SSW IPilot
In i tializeDisk
~Filed on: [Iris] (Lynch >Scavenger,Memo
Copies: Archives Belleville Bergsteinsson Bewley Clark DeSantis
Harslem Heinrich Irby Kennedy LeCcsne Liddle
Lynch Mendelson Metcalfe Reilly, D. Reiiy, J. Schwartz
Sonderegger Szelong Thacker Townsend Wallace Weaver
Wick Wickham White
Copies: Lauer Redell McJones Purcell DClia! Hankins
Jarvis Horsley Murray Kierr Sandman Johnsson
Ogus Garner Bowering
Introduction
The situ2.tion regaidin; ::'.. Scavenger, Copydisk. and InitializeDisk for Oak has been unclear.
This EJemO is in:eIlded to report the current Slatus of those items and to propose a
resoi\.~:ion of lhe it;2ITiS.
D-efini~ions
lni:i<:liz<:Disk (Pilot) - A program which takes a Vlrgm disk f:'om the manufacturer and
formats it into a Valid Pilot Disk containing no Pilot files.
Valid Pilot Disk - a disk pack which has been formented with lh~ proper header, label, and
data blocks. In addition, bad spots have been identified, marKed ~lt1ct removed from service.
Valid Pilot Volume - A Valid Pilot Disk which additionally conLlins a proper Pilot Volume
as described in [Iris]PilotVo!umeFormaLmemo (attached).
Copydisk (Alto) - An existing Alto program which makes a bit-for-bit copy of one disk
pack on another.
Copydisk (Pilot) - A Pilot application client which makes copies of all of the files on the
source Pilot disk upon the target Pilot disk. This differs from a bit-far-bit copy in that
multiple Fl Ds for mutable Pilot files mllst be avoided.
Movedisk (Pilot) - A Pilot application client program which makes a bit-For-bit copy of
one Pilo~ disk pack on another. 1t differs frol11 the Alto Copyd:'~k in that the source pack
must be ~rased or otherwise made permenantly unavailable so [!s lu avoid duplicate FIOs for
the same J1lUl:lble Pilol fi Ie. This shollid be lIsed only when a pack contains only immutable
[Iris] Scavenger.Merno June 15, 1978 3
a) Bad Spots - The current scavenger cannot deal with bad spots. Mike Overton is
slowly accumulating unusable disks that have bad spots on them. As a result I am
placing low priority on dealing with buct spot problems in Oak.
b) Disk Alignment - This is now tess visable as many more people have their own
Altos and packs are shifted less frequently. Jim had a scheme worked out (the
details of which he could not recall on the spot) which would detect incipient
misalignment before it became a real problum. It required co-operation' from the
drive manufacturer.
c) Power Supply run-away - Many problems could be attributed to.. misbehavior on
the part of the power supplies, causing bad writing on the disk. (I would catagorize
our problems with IFS during power failures here)
d) Processor Overload - The Alto has had problems with the microcode tasks not
reacting within real time constraints under unusual circumstances. (There is an
infamous bug which caused every sixth FTP page to be badly writen due to a
combination a microcode tasks collectively taking too much time.)
e) The generation of UIDs is poorly done (it's more like a bug) causing more than
one file to have- that same DID. This complicates life for the Alto Scavenger. Jim
agrees that Pilot has that problem designed out. The problem has never been
corrected orr the Alto simply because the system is not being maintained (the specific
problem seems easy to fix).
Proposal
1) Steve PurceH is to be directed to specify, document, package, and deliver to Oak alpha test
an InitializeDisk. In Oak it will not deal with bad spots.
2) Tne current Alto Copydisk be used as the Pilot Movedisk in Oak. This will be run on an
Aha. Removing the old pack from circulation will be accomplished by operational
procedures. No Pilot Copydisk will be provided with Oak.
3) That Steve Purcell be directed to specify, document, and deliver a Pilot File Scavenger
which is restricted to reconstruction of the vfm and yam. Neither a Pilot Disk Scavenger
nor a Star Scavenger will be delivered with Oak.
June 15, 1978 4
To Distribution Date June 13, 1978
From Stephen Purct:!ll Location Palo Alto
Subject Pilot Volumo;;l Format Organilation SDD/SD
,,!;r-ROX
"
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Filed on: [Iris]PilotVolumeFormat.memo
This memo describes some aspects of Pilot Volumes. Since the design of Pilot and its
volumes is still in flux, only a snapshot of the current design and implementation can be
provided. There is no guarantee that what follows will not change. The general structure is
probably correct and will remain, but many details will change.
Pilot stores files in volumes which are physical disks with data conforming to certain
constraints. Pilot assumes the storage to consist of pages randomly accessed by volume-
page-numbers which range continuously from zero to the size of the volume in pages. Bad
Pages will be hidden by the disk driver. A single disk Diablo 31 will have volume pages in
the range [0 .. 4872). As far as Pilot's volume manager is concerned, a page is an 8 word label
and 256 words of data. This memo ignores additional page fields such as the 2 word address
header used 'by the device drivers/controller.
Pilot partitions pages into a number of files, each with a unique identifier (UniversaIlD) and a
type. (The generation and registration of types is still fuzzy, but many files can have the
same type). (The file properties of immutable and temporary lllay be viewed as contained in
t:he type, althougll they are actually independent fields.) Pilot uses four types for system or
VO!Urr.e files, presem on every volume. Each page in a volume belongs to exactly one file
and has a label with Ihe file ID, the file type and the file-page-number. A client file has
pages vdth consecu:;\:; file-page-numbers from zero, while a system file is numbered by
YG!L:!Ue-page-numbers. which are not necessarily consecutive. Page labels and page data are
stcred together for safety. For efficiency and redundanq. label inform:.lt~n is also stored
in the system files, \"hich can be entirely discarded and reconstructed from labels if
damaged. The four system file types are root, vam, vfm and free. The root file is exactly
one page with a constant location on the volume, containing IDs (and sometimes page
numbers) of the other system files and of one client root file. The vam (volume allocation
map) is a bit map telling which pages are free. The vfm (\'olume file map) is a B-tree
which maps (file 10, file-page-number) keys into volume-rage-numbers for all client files.
The frce file has blank pages scattered over the volume that are not in use t:ither by clients
or by Pilot. Bad pages can be thought of as free pages but the Pilot volume manager is not
aware of them, since the disk driver ensures that there is a good page for every volume-
page-number.
The root file is created and accessed by
LogicalVolume,RootAccess: PROCEDURE[volume: Volume,ID, proc: PROCEDURE[Volume:
LogicalVolume,Handle] ];
LogicalVolume,Hanc!le: TYPE:: POINTER TO LogicalVolume,Descriptor;
LogicaIVolume.Descriptor: TYPE:: RECORD[
version: CARDINAL,
[Iris] with file-page-numbers in J closed-
open interval: [ .. ). The null volume page resulting from initialization or deletion signifies
the absence of a file or a page of a file. Entries have unique keys. and insertions overwrite
existing entries. Therefore pages with duplicate It) and p~lge number cannol be pointed to
by the map. A scavenger would have to deal with such (illegal) p3ge pairs before updating
the vfm. The vfm does nct depend on consecutive file-p:lge-nul11bcrs so that as it is being
reconstructed, say by the scavenger, it can contain fragmcrns of files. Client files.with gaps,
hO\vcver, are not permitted in a legal Pilot volume. Insertions are most efficient \vhen
clustered by key (ordered by TD, page number). GetN8xt is It)cd as an enumerater. All
client file pages can be located on the volume in random aCCt:ss fashion by use of the vfm.
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