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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.

Joseph Kern
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dchochan
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2 Answers2

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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.

neutrinus
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All data transfer between the Server and the SAN happen over the network.

All data transfers between two Servers happen over the network.

If two servers mount the same disk, the iSCSI communication still happens over the network, but you may reduce the overhead of the server to server communications. But now you might have locking issues on the shared filesystem.

Network transfer in any case (client to client, server to client) is always dominated by the slowest network link speed.

Joseph Kern
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