RAID and File Organization - CMSC 424 Final(Complete solutions)

RAID (redundant array of independent disks) correct answers Disks are cheap; Failures are costly; Use extra disks to ensure reliability; faster access to data RAID 1 correct answers A copy of each disk is kept. Can read from any disk. Must write to both. RAID 5 correct answers Distribute parity blocks instead of bits; Read directly from disk; Writes need to read and update parity block How to update 9 to 9' in RAID 5 correct answers Read 9 and P2 P2' = P2 xor 9 xor 9' Write P2' and 9' What to do when disk 3 fails in RAID 5 and you want to read block 1 from disk 3: P0 | 0 | X | 2 | 3 correct answers 1 = P0 xor 0 xor 2 xor 3 Which has better write performance: RAID 1 or RAID 5? correct answers RAID 1 does RAID 1: 2 block writes RAID 5: 2 block reads, 2 block writes to write a single block (think 9 to 9') Which has better storage cost: RAID 1 or RAID 5? correct answers RAID 5 Which should you use for apps with low update rates and large amounts of data: RAID 1 or RAID 5? correct answers RAID 5 What is the buffer manager? correct answers Software layer responsible for bringing pages from disk to main memory How does the buffer manager work? correct answers If block already in memory, return a pointer If not, evict a page and then make a request to fetch necessary block What does the buffer manager do when evicting a page? correct answers Write it to temporary storage Write is back to original location Toss if clean (unmodified) LRU vs MRU correct answers MRU may be better when dealing with sequential flooding; less misses Buffer Manager: pinning correct answers Pinning a block refers to not being allowed to write back to disk