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Server+ Certification Exam Notes

 

Server+ Certification awarded by CompTIA organization is a widely recognized certification in the area of server technologies.  To attain Server+ certification, one need to score at least 75%. These exams basically test the Knowledge in the areas such as Server installation, configuration, maintenance, troubleshooting, and SANs among others. The exam consists of 80 questions and a maximum allowable time of 90 minutes. For further details, you can visit the official website here.  

1. Acronyms:  Click the hyperlink to view commonly used acronyms in Server certification.

2. SCSI bus width:

-          For a 16-bit Wide SCSI, there are 16 possible SCSI Ids, 0-15.

SCSI 3 ultra-wide - 16 devices, 0=bootable drive, 15=controller

-          A standard 8-bit SCSI can support only 8 devices (including SCSI card), the Ids allows are 0-7.

SCSI ID - 0=bootable drive, 7=controller, 1-6=any other devices

3. If the termination is not done, a SCSI devices on the bus will not function properly. This is due to reflection of the signals at the end of the bus. To prevent this, both ends of the SCSI bus need to be terminated. If one end of the SCSI bus is terminated, you may find intermittent problems. Never terminate the bus at a device connected in between.

4. LUN stands for Logical Unit Number. LUN is used to identify a logical device that is an independent functional part of a SCSI device. SCSI-2 specification allows 8 logical units for each SCSI device address. The logical unit addresses are numbered 0 to 7.

5. SCSI Types:

SCSI Type

Transfer speed

bus

SCSI-1

5MBPS

8 bit bus

Fast Wide SCSI

20MBPS

16 bit bus

Wide Ultra SCSI

40MBPS

16 bit bus

Ultra2 SCSI

40MBPS

8 bit bus

Wide Ultra2 SCSI

80MBPS

16 bit bus

Ultra3 SCSI or Ultra 160

160MBPS

16 bit bus

Ultra320

320 MBPS

16 bit bus

6. Important Disk RAID levels:

a.      RAID 0: Disk Striping without parity. Minimum 2 disks are required. RAID 0 doesn't provide any fault tolerance, but read/ write to the disk will improve

b.      RAID 1: Disk Mirroring and Disk Duplexing.  Disk Mirroring requires at least two partitions of same size. Each partition should be on a different physical drive. In other words, minimum 2 disks are required. For disk duplexing minimum 2 disks and 2 controllers are required. RAID 1 provides good fault tolerance, though disk access is slower compared to disk striping.

c.      RAID 2: Disk Striping with Error correction.  

d.      RAID 3: Disk striping with error correction code stored as parity 

 This  takes a striped array as in RAID 0, then adds a parity hard disk drive to the array.  This parity information is vital if one drive fails. If a drive should fail in this situation, the parity drive can be used to restore blocks that have been broken due to data corruption.

e.      RAID 4: Disk striping with large blocks allocation.  

f.       RAID 5: Disk Striping with Parity. Disk Striping with Parity requires at least three partitions of same size, and each partition should be on a different physical drive. In other words, minimum 3 disks are required for disk striping with parity. Fault tolerant, less expensive than disk mirroring. If more than one disk fails, data can't be recovered. You still need to depend on tape back up for multiple disk failures.

RAID 5 is similar to RAID 3, except the parity information is spread across all drives, this allows all drives to be able to rebuild the array if a drive fails. In RAID 3 parity is written to only one drive.

Note that, compared to disk striping or disk striping with parity; Disk mirroring has more overhead, as the entire disk get copied to another disk.

7. RAID 10 describes Mirrored Striping. It is a mode 0 array, plus a mode 1 array, striped. For example, if you have striped data into two drives, each drive is mirrored in RAID 10. That is a total of 4 drives.

8. SCSI Cables:

Types of cabling used for SCSI:

-          8-bit Internal device SCSI connection: Uses Unshielded 50 pin ribbon cable

-          8-bit External device SCSI connection: Uses DB-25 or Centronic-50 cable

-          8-bit External device Fast SCSI connection: Uses mini sub-D connector cable

-          8-bit cables are considered A-cable by SCSI-2 definition.

-          16-bit Wide SCSI uses P-cable or (A-cable + 68 pin B-cable)

-          32-bit Wide SCSI uses Q-cable plus P-cable

Cable lengths used by SCSI devices are:

-          Single Ended (or un balanced) electronic signaling: 6 m 0r 20ft (apx.)

-          Differential signaling (HVD-High Voltage Differential): 25 m or 82 ft (apx.)

-          Differential signaling (LVD - Low Voltage Differential): 12 m

-          SCSI system uses the following types of terminations:

1.      Passive: Uses passive resistors, not recommended usually.

2.      Active: This terminator has a voltage regulator that ensures the correct termination voltage.

3.      Forced Perfect Termination (FPT):A better implementation of active termination that clamps to the output of two regulated voltages.

9. Each device in a SCSI chain needs to have unique ID. For a 16-bit Wide SCSI, there are 16 possible SCSI Ids, 0-15. A standard 8-bit SCSI can support only 8 devices (including SCSI card), the Ids allowed are 0-7.

10. RAID is implemented across several platforms: SCSI, FIBRE-SCSI and IDE are the most common implementations of RAID technologies.  

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