Data Management for Decision Support Session-5 Prof. Bharat Bhasker
Server Hardware Architecture Disk Technology -- RAID The DISK (i.e. I/O ) speed has not kept pace with the CPU speed I/O throughput is the weakest link in the chain Greatest Possibility of Failure => loss of data What is required? A Robust reliable, possibly failsafe storage mechanism Devices with better I/O throughput
Server Hardware Architecture Disk Technology -- RAID Redundant Array of Independent Disks –Cheap (Small) disks can be combined to offer large storage –Plug and Play –Hot Swappable –Reliability and Availability –Disk Block Access = Seek Time + Block Transfer Time
Server Hardware Architecture Disk Technology -- RAID RAID- I Disk Mirroring/ Shadowing Based on VMS shadowing - uses two disks in place of one Both disk contain exact same copy of the data It’s a constant backup/shadow/mirror require twice the disk drive VMS model has common failure point RAID-1 has independent drive/controller/power
Server Hardware Architecture Disk Technology -- RAID RAID- 3 Data Stripping for fault tolerance Doesn’t require twice the disk for backup/mirroring Based on Parity drive I.e. one extra drive for recreating the data Assume five drives for data then RAID-3 needs 6 drives Stripping done at byte/bit level ? 42
Server Hardware Architecture Disk Technology -- RAID RAID- 4 Data Stripping for fault tolerance Stripping done at Block level Better performance Assume five drives for data then RAID-3 needs 6 drives Parallel Reads from Multiple heads ? 42
Server Hardware Architecture Disk Technology -- RAID RAID- 5 Data Stripping for fault tolerance Stripping done at Block/record segments level but parity is rotated In RAID 3/4 all drives used for reading/writing RAID 5 ability to read as many drives as it needs at the same time for different individual read/write requests
Data Organizations Operations on organized data –Find (Locate) –Read (Get) –FindNext –Delete –Insert –Modify –Findall –Find Ordered
Data Organizations Unordered File Organization Find - Average b/2 O(b) Read - O(1) Insert (1) Modify O(b) Delete O(b) A v b x c d w e
Data Organizations Ordered File Organization Find - O(log b) Read - O(1) Insert O(b) Modify O(log b) Delete O(log b) A b c d f t u v
Data Organizations Primary Index an ordered file with fixed record length and two fields- key field and block pointer field. Primary index is built on ordering key field. A b c d t A f j t f j
Data Organizations Assume 30,000 records Blocksize =1024 bytes and R =100 bytes Each block can store 1024/ records. Total block b = 3000 In Ordered files log (3000) = 12 block accesses Ordering Key =9 bytes and Block pointer 6 bytes Primary Index R = 15 bytes records per block 1024/15 = 68 Blocks required to hold 3000 entries 3000/68 = 45 blocks log2 (45) = 6 block accesses + 1 for data block
Data Organizations Clustering Index an ordered file with fixed record length and two fields- key field and block pointer field. Primary index is built on file ordered on a non-key field. A A A d t A d j t d d j j
Data Organizations Secondary Index an ordered file with fixed record length and two fields- non ordering field and block pointer field. Secondary index is built on non ordering field (dense). A b c d t A b c d x e e t
Data Organizations Assume 30,000 records Blocksize =1024 bytes and R =100 bytes Each block can store 1024/ records. Total block b = 3000 In Unordered files 3000/2 = 1500 block accesses Ordering Key =9 bytes and Block pointer 6 bytes Primary Index R = 15 bytes records per block 1024/15 = 68 Each record requires an entry Blocks required to hold entries 30000/68 = 442 blocks log2 (442) = 9 block accesses + 1 for data block = 10 Block accesses
Data Organizations Multi Data Pointers for Duplicate handling Multi Level By creating a primary index on top of the base level secondary index 442 blocks of ordered data can be addressed by primary key mechanism of 68 entries per block 442/68 = 7 log (7) = 3 for locating the block in the secondary level + 1 for secondary level + 1 for data = 5 block accesses