STORAGE

STORAGE:

SAN: (Storage Area Network). SAN is storage connected in a fabric usually through a switch. So that there can be easy access to storage from many different servers. From application or OS point of view, there is no difference in the access of storage if its SAN or storage that is directly connected. A SAN supports block access to data just like directly attached storage.

SAN is faster compared to NAS. It gives good speed and performance. SAN can be considered as a technology that combines the best features of both DAS and NAS. As SAN is a block level storage solution, its best suited for high performance data base storage, email storage etc. Most modern SAN solutions provide, disk mirroring, archiving backup and replication features as well.

NAS: ( Network Attached Storage). NAS is slow. It can not be used for high performance application. NAS is cheaper. NAS is less complex compared to SAN. TCP/IP is only requirement for NAS.

NAS will be using an ethernet connection for sharing files over the network. The NAS device will have an IP address, and then will be accessible over the network through that IP address. When you access files on a file server on your windows system, its basically NAS.

The main downside of using NAS is its performance issue, and dependency on network(most of the times, the LAN which is used for normal traffic is also used for sharing storage with NAS, which makes it more congested)

Major Difference Between SAN and NAS:

SAN	NAS
Block level data access	File Level Data access
Fiber channel is the primary media used with SAN.	Ethernet is the primary media used with NAS
SCSI is the main I/O protocol	NFS/CIFS is used as the main I/O protocol in NAS
SAN storage appears to the computer as its own storage	NAS appers as a shared folder to the computer
It can have excellent speeds and performance when used with fiber channel media	It can sometimes worsen the performance, if the network is being used for other things as well(which normally is the case)
Used primarily for higher performance block level data storage	Is used for long distance small read and write operations

RAID:

LEVEL of RAID:

AID LEVEL: 0, 1, 2, 3, 4, 5, 6 10,

RAID LEVEL 0:

Minimum disk required is 2. Blocks striped/split, No Mirror, No Parity between disks. Blocks are striped so it enhance the performance. But generally it is not used in production environment. Because if one disk is corrupted, we will have data loss i.e it is not fault tolerant.

   

RAID LEVEL 1:

Minimum disk required in 2. No striped, Mirroring, No Parity. Mirroring helps in gaining the redundancy but performance will be slower for large disks as there blocks are not stripped and no parity is included. We will have backup of disks but performance will degrade in this sort of RAID.

RAID LEVEL 5:

Minimum disk required is 3. Here we have striped and parity among the disks. It is widely used in production servers. The read is very fast as data are striped. Write is slow because of Parity present. Disk can be recovered if any of the disk is corrupted because of the presence of Parity. Mostly used because of performance and availability(fault tolerance) and less cost compared to RAID 1+0 and RAID 0+1. Read oriented query are more preferred with this RAID.

If a disk gets an error or starts to fail, data is recreated from this distributed data and parity block— seamlessly and automatically.
Different types of RAID 5 configuration are:
a. Left synchronous
b. Right synchronous
c. Left asynchronous
d. Right asynchronous

RAID LEVEL 1+0: 

Minimum disk required is 4. Here we have good performance but it is very costly. Disk one and two are mirrored. And disk 3 and 4 are mirrored. And disk 1 and disk 3 are stripped.

RAID LEVEL 0+1:

Minimum disk required is 4. Here we have good performance but it is very costly. Disk one and two are striped. Disk 3 and 4 are striped. And disk 1 and disk 3 are mirrored.

What happens when one of the drive in RAID5. And what happens when two of the drive fails in RAID5?
One disk can be recovered but two disk failing at a time can not be recovered.