released: 04/07, 9:00
due: 04/13, 23:59

Answer the following questions.
Submit your answers to Canvas assignments. There is an entry for this homework.


1. Disk performance

Here is some numbers of a disk, CS5600-Disk:

  --Spindle Speed: 12000 RPM
    note: 
     ** this speed number is per minute.
     ** on average, it takes the disk to rotate half a circle to reach a sector.
     ** So, on average, how long does CS5600-Disk rotate to a sector?
        [this isn't a question you need to answer but one you should think of.]

  --Avg Seek Time, read/write: 5ms / 6 ms
    (note: this is the time moving heads to the right track.)

  --Transfer rate: 64 MB/s
    (note: this is the rate of reading/writing sequential data.
     Assume 1MB=10^6B here.)

When CS5600-Disk reads/writes a sector (512 Bytes), it needs to
(1) move the head to the right track,
(2) wait rotating to the right sector,
and (3) read/write the data.

Questions:

(a) How long would it take to do 500 sector reads, spread out
randomly over the disk (and serviced in FIFO order)?  (2 points)
[Write down your calculation and
write the final result in seconds with two decimal place accuracy.]



(b) How long would it take to do 500 sector writes, spread out
randomly over the disk (and serviced in FIFO order)?  (2 points)
[Write down your calculation and
write the final result in seconds with two decimal place accuracy.]



(c) How long would it take to do 500 sector reads, SEQUENTIALLY on the
CS5600-Disk? (FIFO order once more) (2 points)
[hint: notice that some actions only appear once in this case.]
[Write down your calculation and
write the final result in milliseconds with one decimal place accuracy.]




2. SSD

CS5600-SSD is an SSD that has 1 flash bank, 4 blocks (in the same bank),
and 8 pages (2 in each block).
CS5600-SSD uses the log-structured FTL we learn in class.

The current state of the CS5600-SSD is as follows:

         +---------------------------------------+
 blocks  | block 0 | block 1 | block 2 | block 3 |
         +---------+---------+---------+---------+
 pages   | P1 | P2 | P3 | P4 | P5 | P6 | P7 | P8 |
         +----+----+----+----+----+----+----+----+
 data    | D  | B  | C  | A' |    |    |    |    |
         +----+----+----+----+----+----+----+----+

 mapping: A' => P4, B => P2, C => P3, D => P1

-- A, B, C, and D are four logical pages.
-- Whenever a page gets updated, we add an apostrophe ("'") to their names.
-- For example, after an update to page A, A becomes A'.
-- In other words, (A, A', A'', A''',...) is a series of snapshots to page A.
   But they refer to the same logical page (from a program's point of view).

Questions:

(2 points)
(a) draw the CS5600-SSD status (including the mapping) after running

  write(B')
  write(C')
  write(A'')
  write(B'')




(2 points)
(b) (following the last question) now CS5600-SSD runs a round of garbage
collection which recycles all blocks that do not contain valid pages.
  [updated 04/10: note that this is a naive GC; it **only** "recycles all
   blocks that do not contain valid pages"]
Draw the SSD status after the garbage collection.