SQL Interview Questions: Definitions

Questions:
1) What is a SARGABLE predicate?
2) What is DAS? What is NAS? What is a SAN? Name the two main types of SAN networks. What is the common name for the device used to interface to a SAN?
3) What is a LUN? How is it used with a SAN?
4) What is a RAID? What RAID format is the recommended best practice for SQL Server, and why?
5) What is an INSTEAD-OF trigger used for?
6) What is a LOB?





Answers?:
1) Predicates that do searching, like Year > 2000.
2) Direct Attached Storage, Network Attached Storage, Storage Area Network, Fibre Channel and iSCSI, Host Bus Adapter.
3) Logical Unit Number , Each device(or LUN) on the storage area network (SAN) is "owned" by a single computer (or initiator)
4) RAID (Redundant Array of Independent Disks). A collection of disk drives that offers increased performance and fault tolerance. There are a number of different RAID levels. The three most commonly used are 0, 1, and 5. Microsoft recommends a RAID that would provide the best write performance. For each write request a RAID0 would write once, RAID1 or RAID10 would write twice, and RAID5 would write 4 times. RAID 0 is never recommended, so this leaves RAID10 as the recommended.

Here are the RAIDs:
Level 0: striping without parity (spreading out blocks of each file across multiple disks).
Level 1: disk mirroring or duplexing.
Level 2: bit-level striping with parity
Level 3: byte-level striping with dedicated parity. Same as Level 0, but also reserves one dedicated disk for error correction data. It provides good performance and some level of fault tolerance.
Level 4: block-level striping with dedicated parity
Level 5: block-level striping with distributed parity
Level 6: block-level striping with two sets of distributed parity for extra fault tolerance
Level 7: Asynchronous, cached striping with dedicated parity

5) There are 3 types of triggers: BEFORE, AFTER and INSTEAD OF. BEFORE is used to affect the row before the trigger event executes. AFTER is used to trigger actions are activiated for the affected rows. INSTEAD OF is used to triggers its action for each row in the affected row instead of using the trigger event.

6) Locator OBject.