DEFINITION OF DAS, SAN AND NAS STORAGE
- DAS is a block device from a disk which is physically [directly] attached to the host machine.
- You must place a filesystem upon it before it can be used.
- Technologies to do this include IDE, SCSI, SATA, etc.
- SAN is a block device which is delivered over the network.
- Like DAS you must still place a filesystem upon it before it can used.
- Technologies to do this include FibreChannel, iSCSI, FoE, etc.
- NAS is a filesystem delivered over the network.
- It is ready to mount and use.
- Technologies to do this include NFS, CIFS, AFS, etc.
SAN and NAS
Distinctions
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NAS
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SAN
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Almost any machine that connects to a LAN (or is
interconnected to a LAN via a WAN) may utilize NFS,
CIFS or HTTP protocol to connect to a NAS
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Server class devices that are equipped with SCSI Fibre Channel
adapters connect to a SAN. A Fibre Channel based solution has a
distance limit of approximately 6 miles
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A NAS identifies the data by file name and byte offset,
transfers file data or metadata, and handles security, user
authentication, file locking
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A SAN addresses the da ta by logical block numbers, and transfers
the data in (raw) disk blocks.
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A NAS allows greater sharing of information, especially
among different operating systems
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File Sharing is operating system dependent, and may not exist for
all operating systems that are being used
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File system is manage d by the NAS head unit
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The SAN servers manage the file system
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Backups and mirrors are generated on files, not blocks
(this may save bandwidth and time)
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Backups and mirrors require a block by block copy operation. A
mirrored system has to be either identical, or greater in
capacity (compared to the source)
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