Understanding Cisco Cloud Fundamentals Objective 5.1

Describe storage provisioning concepts

Thick

Thick provisioning is a type of storage allocation in which the amount of storage capacity on a disk is pre-allocated on physical storage at the time the disk is created. This means that creating a 100GB virtual disk actually consumes 100GB of physical disk space, which also means that the physical storage is unavailable for anything else, even if no data has been written to the disk.

Thin

Thin provisioning is a method of optimizing the efficiency with which the available space is utilized in storage area networks (SAN). Thin provisioning operates by allocating disk storage space in a flexible manner among multiple users, based on the minimum space required by each user at any given time.

RAID

RAID (redundant array of independent disks; originally redundant array of inexpensive disks) provides a way of storing the same data in different places (thus, redundantly) on multiple hard disks (though not all RAID levels provide redundancy). By placing data on multiple disks, input/output (I/O) operations can overlap in a balanced way, improving performance. Since multiple disks increase the mean time between failures (MTBF), storing data redundantly also increases fault tolerance.

RAID arrays appear to the operating system (OS) as a single logical hard disk. RAID employs the technique of disk mirroring or disk striping, which involves partitioning each drive’s storage space into units ranging from a sector (512 bytes) up to several megabytes. The stripes of all the disks are interleaved and addressed in order.

RAID 0: This configuration has striping but no redundancy of data. It offers the best performance but no fault-tolerance.

RAID 1: Also known as disk mirroring, this configuration consists of at least two drives that duplicate the storage of data. There is no striping. Read performance is improved since either disk can be read at the same time. Write performance is the same as for single disk storage.

RAID 2: This configuration uses striping across disks with some disks storing error checking and correcting (ECC) information. It has no advantage over RAID 3 and is no longer used.

RAID 3: This technique uses striping and dedicates one drive to storing parity information. The embedded ECC information is used to detect errors. Data recovery is accomplished by calculating the exclusive OR (XOR) of the information recorded on the other drives. Since an I/O operation addresses all drives at the same time, RAID 3 cannot overlap I/O. For this reason, RAID 3 is best for single-user systems with long record applications.

RAID 4: This level uses large stripes, which means you can read records from any single drive. This allows you to use overlapped I/O for read operations. Since all write operations have to update the parity drive, no I/O overlapping is possible. RAID 4 offers no advantage over RAID 5.

RAID 5: This level is based on block-level striping with parity. The parity information is striped across each drive, allowing the array to function even if one drive were to fail. The array’s architecture allows read and write operations to span multiple drives. This results in performance that is usually better than that of a single drive, but not as high as that of a RAID 0 array. RAID 5 requires at least three disks, but it is often recommended to use at least five disks for performance reasons.

RAID 5 arrays are generally considered to be a poor choice for use on write-intensive systems because of the performance impact associated with writing parity information. When a disk does fail, it can take a long time to rebuild a RAID 5 array. Performance is usually degraded during the rebuild time and the array is vulnerable to an additional disk failure until the rebuild is complete.

RAID 6: This technique is similar to RAID 5 but includes a second parity scheme that is distributed across the drives in the array. The use of additional parity allows the array to continue to function even if two disks fail simultaneously. However, this extra protection comes at a cost. RAID 6 arrays have a higher cost per gigabyte (GB) and often have slower write performance than RAID 5 arrays.

Disk pools

A disk pool a software definition of a group of disk units on your system.

A disk pool does not necessarily correspond to the physical arrangement of disks. Conceptually, each disk pool on your system is a separate pool of disk units for single-level storage. The system spreads data across the disk units within a disk pool. If a disk failure occurs, you need to recover only the data in the disk pool that contained the failed disk unit.

Your system may have many disk units attached to it for disk pool storage. To your system, they look like a single disk unit of storage. The system spreads data across all disk units. You can use disk pools to separate your disk units into logical subsets. When you assign the disk units on your system to more than one disk pool, each disk pool can have different strategies for availability, backup and recovery, and performance.

Disk pools provide a recovery advantage if the system experiences a disk unit failure resulting in data loss. If this occurs, recovery is only required for the objects in the disk pool that contained the failed disk unit. System objects and user objects in other disk pools are protected from the disk failure.

Stay tuned!!! for more information to be shared through our blog and please subscribe to our YouTube channel named "youngccnaguru lab".