Monday, November 19, 2018

How Data Moving in Storage Area Network




I have a question about how data moves through a SAN.



For example: Within an iSCSI SAN if Server A is mounted with a SAN disk and wants to copy data to Server B which is also mounted with a SAN disk, does the data transfer happen through the SAN raid/disks or the data moving through network server a --> server b?



In file level storage when using let say's file server in windows environment as long as I understand if we move data from client a to client b using file sharing from file server the data moved using network client a --> client b hence if in client a network slower than client b network the copy process would be as slow as client a network correct?



Sorry for my bad English.


Answer



Yes, you are right. Data flow path:





  • hostA asks SAN for data

  • hostA sends the data (over smb?) to hostB

  • hostB tels SAN to write down the data



SAN doesn't understand file systems, network protocols between hostA/hostB. So the slowest link will limit the transfer.



As a solution to this (and many others) problem, there are network filesystems like Ceph.



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