fibrechannel also cp data is sent to the mirror site at a protocol level higher than the raid level so a conventional widely used network protocol such as tcp ip can be used to transmit the cp data because updates to the mirror volume are accomplished through the raid layer 82 in the destination filer 72 not by the source filer 71 directly accessing the mirror site 39 s disks the destination filer 72 can provide reliable read only access to the mirror volume 77 and can detect and correct errors in the mirror volume 77 furthermore bandwidth consumption is reduced since it is not necessary to propagate checksum and xor data from the source filer 71 to the destination filer 72 in addition because the source filer 71 does not directly update the mirror volume the storage devices that contain the mirror volume 77 do not need to have the same geometry as the storage devices that contain the primary volume 76 the techniques introduced above have been described in the context of a nas environment however these techniques can also be applied in various other contexts for example the techniques introduced above can also be applied in a direct attached storage das environment or in a storage area network san environment a san is a highly efficient network of interconnected.