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what is the difference between SAN,NAS and DAS?

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Have you googled? Wikipedia? – jldupont Nov 5 '09 at 13:36
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OK, so there's significant sentiment among many SF users that "Google it" and friends are not valid answers. But seriously, if you type your exact question into a Google search, I'll be you come up with hundreds of hits for this one. – Graeme Donaldson Nov 5 '09 at 14:10
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One might argue that if by Googling it the only answers he came up with were similar to that itmanagement.com link or overtly wordy/complex, then this was the perfect place to turn to. – kingfish Nov 5 '09 at 14:19
One might argue that if that were the case, it could've been stated in the question. "Hi, I've read X, Y and Z pages I found on Google, but I'm confused about A, B and C". – Graeme Donaldson Nov 5 '09 at 15:01
And yet you yourself said that there is significant sentiment among SF users that "Google it" is not an appropriate response, so perhaps he didn't expect the need to prevent those answers to begin with! – kingfish Nov 5 '09 at 15:23
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migrated from stackoverflow.com Nov 5 '09 at 13:38

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5 Answers

up vote 25 down vote

First it is best to define the difference between a block device and filesystem. This is easier grasped if you are familiar with UNIX because it makes an objective distinction between the two things. Still the same applies to Windows.

  • A block device is a handle to the raw disk.
    • Such as /dev/sda for a disk or /dev/sda1 for a partition on that disk.
  • A filesystem is layered on top of the block device in order to store data. You can then mount this.
    • Such as mount /dev/sda1 /mnt/somepath.

With those terms in mind it's then easier to see the distinction between the following.

  • 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.
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+1 - Great job. Nice articulation of the distinction between SAN and NAS. – Evan Anderson Nov 5 '09 at 15:40
I disagree on the definition of the NAS. What Dan Carley describes is actually a network file system. A NAS is an appliance that provides a network file system. The appliance character is essential. A home-build linux box with an NFS server is NOT a NAS. – dmeister Mar 14 '10 at 10:33
I disagree with your definition of not a NAS. If you build a linux server and use it for storage utilising an existing filesystem and sharing that out using an established network protocol such as CIFS, AFP etc as described in the answer, then it is actually Network Attached Storage. I think that you're confused about the acronym NAS, assuming that the 'A' means Appliance. It is true that a large amount of NAS' are appliances but just because some NAS are appliances, does not preclude all NAS being appliances. – Dan Feb 11 '11 at 9:23
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up vote 5 down vote

While the descriptions from itmanagement.com are ok, I think they could be a little more specific.

With NAS, you're usually referring to something where you mount a shared storage space over a network using protocols like CIFS or NFS. The system on which these are mounted does not see them as local storage, it sees them as network storage. This is important because many programs will not allow the use of network storage for various things.

With SAN, the storage space is mounted via iSCSI or Fiber Channel. You're still using a network to mount the space, but the protocols allow the system doing the mounting to see the space as local storage, thus allowing more programs to use it properly.

DAS is simply storage directly attached (ie, not via a network) to a system. Internal harddrives, USB drives, etc.

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up vote 2 down vote

NAS stands for Network Attached Storage. It differs from traditional, directly attached storage in that, in NAS, the operating system and other software on the NAS product are dedicated solely to data storage.

SAN stands for Storage Area Network. A SAN is a network designed to attach storage hardware and software to servers. SANs generally come in two forms: as a network primarily dedicated to transferring data between computer systems and storage systems, or as a complete system that includes all of the storage elements and computer systems within the same network.

DAS stands for Directly Attached Storage. DAS is generally used to differentiate between storage systems directly attached to a server or workstation and NAS and SAN setups.

from http://www.itmanagement.com/faq/storage-faq/

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up vote 0 down vote

stands for Storage Area Network. A SAN is a network designed to attach storage hardware and software to servers. SANs generally come in two forms: as a network primarily dedicated to transferring data between computer systems and storage systems

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up vote 0 down vote

das - it is direct attached storage. system will have full control on disk.it is local storage. problem using das 1 it cannot use as common storage 2 it is not flexible

Nas - it is n/w attached storage.disk attached over n/w. it can be used used as common storage or shared storage problem in nas 1 it maintain own filesystem called nfs.so we cannot install o.s in nas or we cannot boot from nas 2 When compare san nas performance is low.

San - it is storage area n/w. A dedicated storage network that provides access to consolidated.SANs often utilise a Fibre Channel fabric topology. problems using san 1 cost is very high.so it cannot be used in mid-range company

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