data storage – interview questions and answers – part-1

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What are the different form factor of HDD?

Well, the HDD form factor means different sizes of disks. Most widely used form factor disk areas:
3.5 inch, Hight: 1 inch, width: 4 inch, depth: 5.75 inch
2.5 inch, Hight: ,6 inch, width: 2.75 inch, depth: 3.94 inch

What is Access Time in disk?

Access time = Seek Time + Rotational delay + transfer time

Larger the access time lower the performance of disk.

What is micro second and neno second?

micro second (ms): millionth of second
nano second (ns): billionth of second

What is RAID ? and what is different RAID level?

RAID stands for Redundant Array of Inexpesive Disk
There are different RAID levels, going to explain in one line for each.

  1. RAID 0: support high write but not support HA
  2. RAID 1: support HA but not high performance
  3. RAID 0 + 1: support both HA and High performance
  4. RAID 10: support both HA and High performance
  5. RAID 2: bit level not used in the
  6. RAID 3: block level parity bit used
  7. RAID 4: dedicated disk for parity bit
  8. RAID 5: distributed block level parity bit
  9. RAID 6: distributed block level multiple parity bit
  10. RAID DP ( Diagonal Parity): there are two parity bit one is straight forward parity bit and another based on diagonal parity bit. in this RAID level any 2 of the disk gets fails data still be available it means it support HA (High Availability) mode.

What is goal of RAID ?

There two main goal of RAID which are as:

  • increase performance by striping (distribute data on several disk to distribute load)
  • increase fault tolerance by redundancy (mirroring)

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Different form Factor of HDD

Both disk SSD and HDD designed with same size and shape. There are different form factor of HDD are as:

Form FactorHightWidthDepth
3.5 inch1 inch4 inch5.75 inch
2.5 inch0.6 inch2.75 inch 3.94 inch

What are the different Drive Speed of HDD?

Both disk SSD and HDD designed with same size and shape. There are different form factor of HDD are as:

  • 5400 RPM
  • 7200 RPM
  • 10000 RPM
  • 15000 RPM

What is relations between RPM, capacity, cost and Performance

Thumb rules are:

  • Higher the RPM better the performance.
  • Higher the RPM lower the capacity.

Key points about Capacity, cost, Performance, and Speed

  • usually 10k and 15k RPM drives usually implements SCSI command set and SAS or FC interface.
  • 5.4K and 7.2 K RPM drives usually implements ATA command set and have SATA interface.
  • RPM and capacity are inversely proportional to each other. means if you increase one you have decrease another.
  • Speed and capacity and inversely proportional to each other, meaning that if you have to increase the speed you have to decrease capacity.
  • RPM and Performance are directly proportional to each other , meaning that one increase another will also increases.

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