INF 551 – Spring 2016 Homework #1 Solution USCID: 3791415037 [email protected] 1. [ SSD, 30 points ] Consider an SSD with the following specs on read/write performance. Ignore the latency in all read/write requests. Operation Time Read a page 25 microseconds Write a page 250 microseconds Erase a block 2 milliseconds Consider the following blocks and two requests (in this order): first, inserting two new pages; second, update page 1. State the read/write/erase operations needed to perform these two requests. How long does ittake for them to complete? 1. Insert 2 new Pages For inserting 2 new pages, the whole block is read into cache or RAM and reordered, while the controller erases the entire block, then writes the entire block back out. This will take 3 read operations followed by block erase operation, followed by write operation for 3 old pages + 2 new [total 5 write operation]. More Specifically, 3 Page Read operations: = 3*25 microsec = 75 microsec = 0.075millisec --------------- (1) 1 operation to erase a block = 2 millisec -------------------- (2) 5 write operation = 250 * 5 microsec = 0.25* 5 millisec

= 1.25 millisec ------------------(3) Total time needed to insert 2 new pages (1) + (2) +(3) = 0.075+ 2 +1.25 millisec = 3.325 millisec ------- (4) 2. Page 1 Update This operation is pretty simple one, as we have 1 free Page left in the block. So, rather than updating the Page (Read+Erase+Write), we will just mark Page 1 as stale, and perform only single operation of Write on the Available Free Page. 1 Write Operation: = 250 microsec = 0.25 millisec ------------ (5) Total time needed to perform the operation of Insert of 2 pages and Update of Page 1 = (4) + (5) = 3.325 + 0.25 millisec Ans= 3.575 millisec 3. [ Disk scheduling, 30 points ] Consider a hard drive with 200 tracks (0 to 199). Suppose the head