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GFS Architecture:


Google sorted out the GFS into groups of PCs. A bunch is essentially a
system of PCs. Each group may contain hundreds or even a large number of
machines. In the GFS groups there are three sorts of group: Clients, Master
servers and chunk servers. There is generally just a single master, one or
numerous customers/clients and numerous chunkserver. Backup
master is also present in case the primary master fails.

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Customer – In the
realm of GFS the term ” Client” alludes to any element that ask for a
document. Demand can extend from controlling existing documents to making new
records on the file. Customers can be different PCs or PC application. The
customers are really the clients of the GFS.

Chunk Servers –
ChunkServers are the workhorses of GFS. They are in charge of storing the 64 MB
record lumps. The Chunk Server don’t send the information to the master server,
rather send the information requested straightforward to the customer.


Master – The master
fills in as the organizer for the group. The master obligations incorporates
keeping up operations log, which keep tracks of the exercises of the master
bunch. master keeps up the verifiable record of basic metadata changes,
namespace and mapping. The operation logs causes keep benefit interference to a
base. In the event that the master server crashes, a substitution server that
has monitored the operation log can have its spot. The master server likewise
monitor the metadata which is data about data that depicts the lump. The metadata
information advises the master server to which chunkserver has the data and
where they fit inside general record. It stores three noteworthy sorts – (1)
namespace, document and lump identifier. Metadata is put away in memory.



The GFS duplicates
each chunk in various circumstances and stores it on the distinctive
chunkservers. Each duplicate is known as a copy. Of course, the GFS makes three
copy for each piece , yet client can change the setting and make extra
duplicates of it as and when wanted. The reproductions are not put away in a
similar piece server, it put away crosswise over various Chunk Server so that
on the off chance that one master server is dead/unresponsive, the other can
answer and give the important data to the customer. This system makes the
procedure continually going.


Figure 1 : GFS


Figure 1 clarifies
the stream of the data from the customer to the master and after that to the
chunkserver. The customer/client goes to the  chunk server and ask if it is having the
information. The ace sends chunk index, chunkserver consequently sends a pulse
and tells the master it is alive, When the master thinks about them, it sends
metadata to the customer, on the premise the customer isolates the document
into what he needs, master at that point sends it to the chunkserver.


Read Operation:


The application send
the document name, byte range to the GFS client. The customer changes over the
byte counterbalance given by the application into chunk index. The customer at
that point sends the record name and chunk index to the master. The master
check with the chunk server who has the documents. The master thus restores the
chunk handle and area of the copy to the customer. The customer at that point
straightforwardly contact the chunk server with the chunk handle and byte run.
The chunk server at that point exchange the information to the client . The
master isn’t engaged with the information exchange process so master does not
turn into the bottleneck of the procedure.


Write operation: The
application sends the document name and the information to the customer. The
customer sends the document name and chunk index to the master. The master
check with chunk if it  has the control,
on the off chance that nobody has the control, master doles out the control to
a chunk, that turns it into a primary chunk server. The master at that point
send the file location and chunk handle  to the application. The client sends data to
every one of the copies. The essential in the wake of getting the information,
sends a positive reaction to the customer. The customer sends the write charge
to the primary. The primary sends the data write summon to the two optional
copies in serial request. After the information is written, the auxiliary
answers back to the primary and recognize the write occasion. The primary
affirms to the customer that the compose operation is finished. The
read/compose operations should be possible in parallel by the customer. Figure


Figure 2: Write
information stream operation 

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