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Monday, June 25, 2007

Difference between BLOCK and FILE level Data : -Ashwin

Block refers to Physical level, the way OS interacts with Disk-Drive, simplest example would be "OS interacting with local SCSI Harddrive in our home/office pc" . It deals with block of disk, there is no file-system attached to it. Clients can not read and interepret block-data if there is no internediate file system like ..NTFS, FAT, Ext3 etc.

SQL and Exchange: Are highly write and read intesive databases, in other words, they need faster processing because they process many read and write requests, (Online Transaction Processing) and thats why they deal in "Blocks". Therefore SQL and Exchange database is not recommended on "NAS" or "FIle servers", because these file servers are usually accessed as a mapped or UNC path and the data is moved via "TCP/IP" network and it deals in "File Level" protocol such as "CIFS/SAMBA" for Windows and NFS for (UNIX/Linux) paltforms which is not suitable for Databases applications.Block storage is normally abstracted by a file system or database management system to talk to clients or endusers.


Block based databases requires : Locally attached disk array Or SAN data centers.


File Level Data: The data which has file system attached, for example: a word document , is a file level data and is backedup along with this meta data. This is where NAS / Netapp / Windows Storage Server comes in to picture, they are basically "Read" intesive boxes. They are not meant for intensive writing, they are basically file servers providing file service (Read) to clients. For normal disk sharing between small Office / Home office this is a good option, where many users can write to and read to common "Disk" on the remote server via mapped or unc path.

File level : NAS / Netapp & Windows Storage Server.


Summary:
This file system can reside either on a server or on a NAS device. If it’s on the server, block level data is written to the disk array, usually via either an FC or iSCSI interface. If the file system is on the NAS, file level data is written to the NAS device, usually via Ethernet. The NAS device in turn writes block level data to disk. A “NAS Gateway” is a device that maintains the file system and communicates file-level data with clients on the LAN, while storing data on external FC-attached disk.

An advantage of file level data is the ease of sharing information. Because the file system resides within the NAS, any device can access and understand the data. When the file system resides in the server, only that server can retrieve data from the disk.


BLOCK vs FILE - WHAT HAPPENS UNDERNEATH


FC-SAN communicates at the block level, with requests over the "wire(fiber/copper)" like :

•Read-block-thirty-four
 
or
 
•Write-block-five-thousand-and-two
 
 
 
NAS communicates at the file level, with requests over the "wire (Ethernet)“  like:
 
 
•Create-file-MyHomework.doc
 
or
 
•Read-file-Budget.xls
 
 
 
 
The Wires being used:
• NAS solutions utilize TCP/IP based networks, such as Ethernet
 
• SAN solutions use Fibre Channel connections (Fiber/Copper)
 
 
 
 
 
The Protocols being used:
 
• NAS solutions use  iSCSI Protocol over standard Ethernet networks to talk BLOCK.
 
• SAN solutions utilizes Fibre Channel encapsulated SCSI setups

 

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