GFS not stop.[2] For disaster recovery and information safety,

GFS Architecture:


The architecture contains different kind of entities they are as listed

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 Master server


There is generally a master, one or numerous customers/clients and
numerous chunkserver. Backup master is also present in case the primary
master fails. 1


Client – Application
and personal computers are the clients. Client can request to add or edit a
file 2

Chunk Servers –They are
the critical part of architecture, which do most of the hard work and save the information
in chunks . Chunks are 64 mb in size that is usually a big size, good enough to
store most of the file type. The Chunk Server always sends the information
straight to the application and does not involve master in the data send
activity. The master is mostly involved in the control flow activities. 1


Master – All the
activities are monitored by the master. The master coordinate the clusters and
modify the operation log1 The log is used by the master to note down its
action. For troubleshooting, the logs are very important as it points where the
failure and what time the failure happened. Master stores the changes in the
metadata. Master sends delete and create new chunk request to the chunkserver.
We can treat the master as the store house, it stores the mapping details and
the namespace of the chunks. The operation log is always monitored, if logs are
not getting updated, the system understand that something is wrong an d may be
the master is not alive, in this scenario, quickly an assistant server takes its
place so that the operation does not stop.2 For disaster recovery and
information safety, GFS makes several copies of each chunk and keep them in
different chunk server. Each duplicate is known as a replica. Initially the GFS
makes three copy for all chunk, master has the control on the setting to make
extra duplicates of it as and when wanted. The data are not put away in a
similar chunk server, it put away crosswise over various Chunk Server so that
on the off chance that one master server is dead/unresponsive, and remaining
chunkserver can answer and give the important data to the customer and it
important for the procedure to keeping running2The master server uses the
metadata to identify which chunkserver has the information the client is
looking for and which chunk has the information. Collection of the abandoned
chunk is also the responsibility of the Master1


Figure 1 : GFS


Figure 1 demonstrates
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 master 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.  1

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
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. 2


Write operation: Figure
2  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 client
that the compose operation is finished. The read/compose operations can be done
in parallel by the customer. 2


Figure 2: Write
information stream operation

1 The Google
File System Sanjay Ghemawat, Howard Gobioff, and Shun-Tak Leung Google?