Question

1. Consider a demand-paging system with the following time-measured utilizations: CPU utilization 20% Paging disk 5% Other I/O devices 97%
Indicate which will improve system utilization and explain your answer.
  
a. Install a faster CPU .

b. Install a bigger paging disk.

c. Increase the degree of multiprogramming.

d. Decrease the degree of multiprogramming.

e. Install more main memory.

f. Install a faster hard disk or multiple controllers with multiple hard disks.

g. Add prepaging to the page-fetch algorithms.

h. Increase the page size.

2. How is X-RAID or Hybrid RAID different than regular RAID levels?

Answer 1

a) This will increase the amount of CPU usage per unit time. Because the

paging disk is saturated with requests, this implies that RAM is inadequate for

the number of processes currently running. Thus, if we were to decrease the

number of processes running, it would make more physical memory available

to each process, so there would be fewer chances that the processes would

page fault. Fewer page faults mean less paging disk accesses, which means

less time spent by the CPU waiting for disk I/O

b) This will definitely increase the amount of CPU usage. Since more memory

is available to each process, more pages for each process can be in RAM

simultaneously, and there is a lower probability that any given process will

page fault. As stated before, fewer page faults mean fewer paging disk

accesses, which means less time spent by the CPU waiting for the paging disk.

c) Again, this depends on the processes, but it may improve CPU utilization.

If processes are continually page-faulting on logically adjacent pages, then

increasing the page size will result in fewer page faults, and therefore less

disk access time and less CPU idling. However, if this is not the case, then

increasing the page size will only worsen the problem, since more time will be

spent by the paging disk reading in data or code that will not be used anyway.

d) This will probably not increase CPU utilization — on the contrary; it will

probably decrease it. The given data suggest that most of the time the CPU

is idling, waiting for the paging disk to complete its task. Since the CPU

is dependent on the paging disk, installing a faster CPU will only cause

processes to execute more quickly and place a greater demand on the paging disk

e.)  likely to improve CPU utilization as more pages can
   remain resident and not require and not require paging
   to or from the disks.
f.) Install a faster hard disk or multiple controllers with multiple hard disks.
   it is also an improvement as the disk bottleneck is removed by
   faster response and more throughput to the disks. the CPU will get
   more data, more quickly

2)Now you know what SHR and RAID are, what is now important is which should you choose. Both are excellent methods of redundancy and have their own benefits. But lets take a look below at their strength and weaknesses:

SHR Strengths

• Faster to setup
• Expandable
• Ability to mix drives
• Greater available capacity when mixing drives whilst still maintaining 1 disk of redundancy
• If a drive fails, the Synology can still access the full volume data – though will operate much slower till a replacement drive is installed
• Drives can be carrier over to a new SHR supported Synology and the new NAS will see the volume and the data

SHR Weaknesses

• A little slower than traditional RAID but equal speed to RAID 5 and 6
• You cannot remove the Drives in an SHR RAID and install them in a new non-SHR NAS, they will need to be formatted.

And now onto Traditional RAID

RAID Strengths

• Broader options for deployment. More task specific RAID sets like RAID 10 or RAID 50 are possible
• Better chance of Hard Drives being recognized in a new NAS/DAS enclosure if you install them in a new unit
• Still scalable between RAIDs, but not as much as SHR
• On the whole, better Read and Write speeds available
• Not just limited to Synology

RAID Weaknesses

• You cannot effectively mix drives and to increase the total capacity will in all likelihood only be possible by replacing ALL drives in the array
• Cannot access the data after a drive failure until a new drive is installed (exception of RAID 1)
• Takes noticeably longer to create a RAID array compared with likewise SHR