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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