Retrieval Multimedia Data from Disks

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Retrieval Multimedia Data from Disks Presented by
Yuni Xia
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• Fundamental characteristics
• Real-time storage and retrieval
• Large data transfer rate and storage space
  requirement

• Why choosing magnetic disk
• Storage capacity
• Speed
• Moderate cost / Random access / Writing

3
Side View
platters
Read/write head
Spindle
Top View
Tracks
Sector
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Symbol Meaning
tnum snum itd ss rv dtr
total of tracks total of sectors intertrack
distance spin speed radial velocity data
transfer rate
Suppose Wish to read data sector i on track ti,
read head is currently over sector j in track tj
Readtime seek(ti, tj) rotation(si,sj)data/dt
r seek(ti, tj) abs(ti-tj) / rv
rotation(si,sj) (abs(si-sj) / snum ) / ss
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• Raid arrays and Placement methods
• By spreading data across several hard disks
• faster performance
• greater storage capacity
• higher data security

• Six standards 0-5
• (cross-type variations, such as 0/1, 3/5)

• Implemented by software and hardware

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RAID 0 Striped Disk Array without Fault
Tolerance RAID Level 0 requires a minimum
of 2 drives to implement
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
etc..
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RAID 1 Mirroring and Duplexing RAID
Level 1 requires a minimum of 2 drives to
implement
A
E
I
M
A
E
M
I
B
F
J
N
B
F
N
J




C
G
K
O
C
G
O
K
D
H
L
P
D
H
P
L
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RAID 5 Independent Data Disks with Distributed
Parity Blocks RAID Level 5 requires a
minimum of 3 drives to implement
A0
B0
C0
D0
0 parity
A1
B1
C1
1 parity
E1
A2
B2
2 parity
D2
E2
A3
3 parity
C3
D3
E3
4 parity
B4
C4
D4
E4
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A model of heterogeneous disk servers
Router
Server1
Server n
. . .
...
...
d1
d2
d3
dm
d1
d2
d3
dn
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• What needs to be modeled?
• The intrinsic characteristics of each disk
  server
• The intrinsic characteristics/capabilities of
  each client
• The relationship between the disk servers and
  clients
• The distribution of data across the disk server

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Disk Server Characteristics 1. Dtr(i)
Total disk bandwidth of disk server i 2. Buf(i)
Total buffer space associated with server
i 3. Switchtime(i, t) Time required for si
to switch between clients at time t 4. Cyctime(i,
t) One cycle of read operation to be
executed by si at time t
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Client Characteristics 1. Cons(i,t) The
consumption rate of client Ci at time t 2.
Data(i, t) (M, b) Play data(i, t)
(m,b), (m, b1), FF data(i, t)
(m,b), (m, bffs), (m, b2ffs), RW
data(i, t) (m,b), (m, b-rws), (m, b-2rws),
Pause data(i, t) (m,b)
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Client Characteristics Data(i, t) (M, b, len,
step) b, (bstep), (b2step), . ,
(b(len-1)step) 1. Play step 1
2. FF step ffs 3. RW step -rws
4. Pause step 0
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• Client-Server Characteristics
• 1. Timealloc(i,j,t)
• In any given cycle of disk server i, each
  client
• cj has a time-slice, timealloc(i, j, t)
• cyctime(i, t) gt sum( timealloc(i,j,t))
• (ni,t switchtime(i,t))
• 2. active(t)
• The set of all clients that are active at time
  t.
• 3. d_active(i, t)
• active(t) Union(d_active(i, t))

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Client-Server Characteristics 4. Ut (i) The
set of servers which are handling the requests of
client Ci. Ut (i) S Ci d_active(s,
t) 5. Bufreq(j, i, t) The amount of buffer
that is required at server Si so that data that
client Cj needs to read doesnt get
overwritten. Buf(i) gt sum(bufreq(j, i, t)
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• Distribution of Data
• M (mi , b) placement mapping
• The set of all servers that contain block b of
  mi
• M ( Sound of Music, 20 ) 2, 4, 5
• Placement constraint
• data (C, t) (m, b, len, step) i (0lt
  i ltlen)
• ( j Ut (i) ) ( j M (mi , b ( i
  step ) )

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Suppose Data (C, t) (M, 5, 5, 3),
Ut (C) 1, 3, 4 5, 8, 11, 14, 17
must be in S1, S3, S4
Definition State of an MOD System S(t) 1.
Active ( t ) 2. Cyctime (i, t) 3. Cons ( i,
t ) 4. Timealloc ( i, j, t) 5. Data ( i,
t) 6. Ut
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Disk availability constraint 1. Consumption Rate
Constraint Sum(cons(j,t)) switchtime(i,t)
dtr(i)/ cyctime(i,t) ltdtr(i) 2. Buffer
requirement constraint sum(buf(j, i, t)) lt
buf (i) timealloc (i, j, t) cyctime (i, t)
cons (j, t) / dtr(i) bufreq(j,i,t)
(dtr(i)-cons(j,t)) timealloc(i, j, t)
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Router
Server1 B 1-150
Server 2 B 151-250
Server 3 B 200-300
...
...
...
(mi, 140, 2, 5)
(140, 145)
(150, 155)
(mi, 199, 2, 1)
(199, 200)
(201, 202)
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Trans Transaction type
Priority
tr1 tr2 tr3 tr4 tr5 tr6
exiting client continuing client-normal continuing
client-needs switching continuing client- needs
splitting new client new client -needs splitting
5 4 3 3 2 1
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• An event-based algorithm QuickSOL
• FindSOL
• OptimizeSOL

FindSOL Phase 1. Split EV(t) into 6 sets
new(t), exit(t), cont(t), pause(t), ff(t),
rew(t) 2. (handle exiting clients)
For each clients Ci in exit(t) do 1) free the
resources 2) delete Ci from state table
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3. (Handle Continuing Clients) For each
clients Ci in cont(t) or ff(t) or rew(t) do
If servers currently assigned to C satisfy
.. then modify the state table else 1)
re-set Cs priority to 3 2) Move it
into new(t) 3) update the resource
table 4. (Handle New Clients) For each
clients Ci in new(t) do 1) Identify the
servers that have the data required by C
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• 2) Determine which server have enough bandwidth
  ..
• IF no such server is available,
• split the event into 2 sub-events
• data(C, t) (m, s, l/2, 2step) and
• data(C, t) (m, sstep, l/2,
  2step)
• Keep splitting till for both sub-events ...
  
• Update state table
• 3) Do the same as 2) in terms of buffer
  requirement

OptimizeSOL phase 1. Switching 2. Splitting
Balancing the load, Maximizing the of
clients ...