c10-2-3

Data layout on disks

Preliminary definitions

strand: a sequence of continuously recorded video frames or audio samples.
frame: basic unit of video.
sample: basic unit of audio.
media block: a sequence of consecutive sectors storing media units.M_i
media gap: the separation between successsive blocks of a strand.G_i

Symbols

Symbol	Explanation	Unit
S_mu	size of media unit	bytes
S_ds	size of disk sectors	bytes
M_i	media block size in storage pattern of strand S_i	sectors
G_i	gapsize in storage pattern of strand S_i	sectors
B_i	buffer size for retrieval of strand S_i	bytes
R_i	size of read-ahead for retrieval of strand S_i	bytes
r_ds	rate of data tranfer to or from disk	sectors/sec
T_tt	track-to-track seek time of the disk	sec
T_rot	rotation time of the disk	sec
T_dis	display time of a media block	sec
L	LCM(M₁+G₁, M₂+G₂)	sectors

Storage pattern

media retrieval of a strand

Storage pattern( M_i , G_i)

Continuity requirment:

Merging the stroage of two strands

storage pattern on disk

merge condition

k₂ x M^'₂ - k₁x G₁ blocks was seprated by ( M^'₂- M₂ -1 ) sectors;
others blocks was seprated by ( M^'₂- M₂ ) sectors.

Example

Determining the read-ahead

basic requirement

further derivation

Determining buffer sizes

minimum continuity requirement

oversatified continuity requirement

need additional blocks

Merging more than two strands

binary merging: ( ..(((s₁s₂)s₃)s₄)....s_n)
strand deletion

after deletion, s'=(M', G') where M' = M - M_s,G' = G + M_s