Data persistence (session persistence) Flashcards
(26 cards)
name a storage device that offers data persistence
Hard disks
types of access to hard disks
- direct/random
- sequential
what is a hard disk made up of?
- spindle
- platters
- read/write head
- sectors
- tracks
What is Multi Zoning
When the outher tracks of the disk have more sectors (circumference is longer)
Define a sector
A sector is the smallest unit of data that can be read or written from a disk
Define a cluster
A cluster is the smallest unit of data that a file system can allocate for a file/ each cluster has a fixed size which is always a multiple of te sector size
Explain external fragmentation
When a file is split into multiple
clusters on different areas of the disk
What is a track
A track is a ring of sectors on a platter. A read/write head can read all the data from a certain track by moving to a position and then rotating the platter
What is a cylinder
A cylinder is simply the group of tracks in all the platters that are on top of each other.
What is rotational latency
rotational latency is the delay, or latency, experienced while the hard disk drive rotates its (platters) to the correct position before it can read or write data
on average, the rotational latency is half the time of a complete turn
what does the time of input/output operations depend on?
- seek time
- rotational latency
- transfer time
Track skew
angular offset should be long
enough to be just greater than seek time required
Interleaving
Jump should be long
enough to be just greater than transfer time required
How does external fragmentation affect reads/access and allocation
- Sequential reads: it interrupts the flow by introducing seek access
- Direct access: no affect but it may break the locality advantage
- Allocation: Altough space is available, its not contiguous
Internal fragmentation
Any data file needs to be spanned into a list of disk blocks
Name a technique for a faster larger and more reliable disk system
The RAID units technique
Explain the RAID units
The technique to use multiple disks in an aggregate to build a faster and more reliable system
What effects a units reliability?
- Number of platters
- Seek usage pattern
- Temperature
- Power consumption
Explain Disk shadowing
Making two or more copies of data written to a disk drive.
Explain Disk Duplexing
A method of storing data whereby the data from one hard disk is duplicated onto another, with each using its own hard disk controller. (in contrast to disk mirroring)
Explain Disk Mirroring
A method of storing data whereby the data from one hard disk is duplicated on another, with both hard disks sharing a single
hard disk controller. (in conntrast to disk duplexing)
Mention the benefits of implenting the use of multi controllers and disk mirroring
This reduced the chances of total disk failure.
How is a general aggregated unit built?
An aggregatedunit is built from a number of simpler disks, CPUs, & RAM
RAID 1 to 5 are the original structures/set ups. how do they differ?
structural layouts for aggreagted units differ in terms of data placement and the type of redundancy built.
