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"What are the differences between Direct attached Storage, Network Attached Storage, and Storage Area Network? Which one is preferred for you and Why?"
- Student from Bilkent University, Ankara, Turkey
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DAS - direct attached storage. This is storage in or right next to your server. You don't share storage resources and you're totally dependent on the capabilities of your server / operating system when it comes to snapshots and mirroring. Most of the time lots of disk space is wasted, because your server simply doesn't need the extra emptry space (yet). Your server mostly uses a local SCSI card to access these disks.
NAS - Network Atatched Storage. This is a "share based storage array". You'll get CIFS or NFS shares from a centralized array. Most of the time you'll access these shares over a LAN network using a dedicated LAN adapter or TOE card. A NAS array is furthermore capable of making snapshots and local as well as remote copies of your data, without your servers knowing you're doing this.
SAN-attached - Centralized storaged which can be accessed over a SAN (Storage Area Network). Some people mistakenly say SAN when in fact they mean a storage array which can be accessed over a Storage Area Network using the Fibre Channel or iSCSI protocol. A SAN is a network and you don't store data on your network, do you ? A SAN attached array is block based storage in which you share a bunch of disks accross a number of servers. If you had to provide each separate server with the disks it needs, based upon performance as well as space, you'll probbaly end up buying way more disks than when you could share these resources with all servers you have. A SAN attached array is furthermore capable of making snapshots and local as well as remote copies of your data, without your servers knowing you're doing this.
The answer to the last question about "which one is preferred": it totally depends on your needs.
If you only have a few servers without the need for smart replicas and shared performance, you might be better of using DAS. If you have a need for centralized shares, you could deploy a fileserver or a NAS. The NAS can have smart replication options, which a fileserver doesn't have. If you need block based access to your data plus the need for a huge amount of disks since you need to share all available performance and space accross all attaches servers, you're probably better of using a SAN attached array.
In a nutshell these are some differences between DAS, NAS and SAN attached storage. There's also CAS: content addressed storage, but that's more a archiving solution using retention times, not a way of accessing the actual data.
My name is Rob Koper and I'm based in the Netherlands, I work for an inovative EMC partner called Open Line Consultancy (www.openline.nl) and we do projects, have long term contracts with customers to remotely support their storage and we place colleagues at customer's sites to help the local admins keep everything up and running.
I'm a proven professionel since 2004 and I hold the following certifications:
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Direct-Attached Storage (DAS) is an architecture where storage connects directly to servers(internal or external).
Network-attached storage (NAS) is an IP-based file sharing device attached to a Local Area Network
(LAN) provide file level access.
A storage area network (SAN) is a dedicated high speed network for block level data access.
-SAN enables storage consolidation and allows storage to be shared across multiple servers.
In contrast to DAS or NAS, which is optimized for data sharing at the file level, the strength of SANs lies in its ability to move large blocks of data.
DAS, NAS and SAN all offer tremendous benefits, but each is best suited for a particular environment, and it is preferable as below:
DAS is ideal for localized file sharing in environments with a single server or a few servers
NAS is an ideal choice for organizations looking for a simple and cost-effective way to achieve fast data access for multiple clients at the file level.
SANs are the best way to ensure predictable performance and 24x7 data availability and reliability.
Amman - Jordan
EMC Proven Professional
(EMCISA) - Information Storage Associate ( 27Feb 2011)
Also good to know: if you need some sort of shared storage (for example, for a cluster or for VMware to be able to do VMotion) you can not use DAS since that is either attached to one or the other server. In that case you need NAS or SAN since both can be used as shared storage device.
Hope this adds to the useful info the others already posted.
This is not entirely true. I've seen 3 node UNIX clusters sharing the same disks using smart SCSI id settings:
Host1 - scsi controller id = 7
Host2 - scsi controller id = 6
Host3 - scsi controller id = 5
disk 1 - scsi id = 4
disk 1 can be shared by all 3 hosts and it's DAS !
I must say that I've seen this set up in 1997 in a SCO UNIX Openserver cluster and I think this solution was called "Wolfpack", but I'm not sure about the name.
@RRR I didn't know about that one, but nonetheless DAS systems are not proposed for shared storage environment requirements today as far as I know... ?
DAS: DAS means direct attached Storage . In lehman terms the storage device that us directly connected to the computing device . For example the HardDisk in your computer.
NAS: NAS means Network Attached Storage. This Storage Device is attached on the Local Area Network and used for sharing of data among different users attached to the Local Area Network . In lehman terms if you are group of students in a college and want a common location to share the music , movies and other studd with each other , you can buy a iomega NAS and connect it to the LOCAL LAN of your college and create a share on the IOMEGA NAS and using the IP of that share every student can put or pull data from that share so it will act as a central repository.
SAN: SAN means Storage Area Network .... As DAS is directly connected to a computer , in SAN storage is connected to various computers and computers get storage from a common storage device or devices which helps in storage consolidation and using the storage optimally . For example there can 3 computers that can be connected to a Storage Device of 1 TB Storage and have dedicated storage from the Storage Device i.e. 100 GB assigned to computer A , 100 GB assigned to Computer B and 100 GB assigned to Computer C. The connection between the hosts and storage is made using specialized switches called Fibre Channel Switches or using iSCSI using the Network Switches.
The differenct between the SAN Storage is that it has a block level access and NAS has file level access . In lehman terms if you have to read a slide from a presentation stored on NAS OS will read the whole file due to file level access and if you have to read a slide from a presentation stored on SAN , OS will read the only the necessary blocks .
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