SAN QUES SET 01

dw-question-answer

1) what is FC controller and disk controller & disk array controller?
A. FC Controller is nothing but HBA (Host Bus Adapter)
The disk controller is the circuit which enables the CPU to communicate with a hard disk, floppy disk or other kind of disk drive.
A disk array controller is a device which manages the physical disk drives and presents them to the computer as logical units. It almost always implements hardware
RAID, thus it is sometimes referred to as RAID controller. It also often provides additional disk cache.

A disk array controller name is often improperly shortened to a disk controller. The two should not be confused as they provide very different functionality.

2) Difference and usage of RAID 0+1 and RAID 1+0
A)I don’t want to write answer again. There are already so many blogs explaining different raids and
there performance.

3)Default ID for SCSI HBA?
A) In a typical parallel SCSI subsystem, each device has assigned to it a unique numerical ID. As a rule, the host adapter appears as SCSI ID 7, which gives it the
highest priority on the SCSI bus (priority descends as the SCSI ID descends; on a 16-bit or “wide” bus, ID 8 has the lowest priority, a feature that maintains
compatibility with the priority scheme of the 8-bit or “narrow” bus).so answer is 7.

4) Highest and lowest priority in SCSI?
A) Each SCSI device is addressed on the bus via a specific number. For narrow SCSI (which allows up to 8 total devices), these are numbered 0 through 7; for wide SCSI
(16 devices) the numbering is 0 through 15. The priority that a device has on the SCSI bus is based on its ID number. For the first 8 IDs, higher numbers have higher
priority, so 7 is the highest and 0 the lowest. For Wide SCSI, the additional IDs from 8 to 15 again have the highest number as the highest priority, but the entire
sequence is lower priority than the numbers from 0 to 7. So the overall priority sequence for wide SCSI is 7, 6, 5, 4, 3, 2, 1 , 0, 15, 14, 13, 12, 11, 10, 9, 8.

5) SAN TOPOLOGY?
A) We have different types of topologies like core edge and mesh topology.

6) How many disks are minimum for Raid 5?
A) 3 disks are minimum for RAID 5.

7)Can Hotspare assigned for RAID0?
A) For Raid0 we don’t have any parity. so there is no point in assigning hot spare since we cannot rebuild data from failed disk.

8) What is HA?
A) HA means High Availbiliy.We do lot of things to maintain High Availbiliy in SAN like maintaining redundan fabrics, raid system, hot spares.
All these things help us in avoiding single point of failures and allows system to handle faults of failures.

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