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SAN (Storage Area Network)

Posted on 2015-01-23
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Dear experts,

I wish to know about setting up the SAN (Storage Area Network) and how it works. I've read the articles upon NAS vs SAN and how SAN can be integrated with servers for sharing hard disk space usage with greater scalability.

My question is that if I setup raid with the hard drives on SAN and allocate the few hundred GB for couple servers will I be able to copy the data from one server to another simply as copy the data from one location of the hard drive to another?

A good example is that if I have a 1TB of hard drive on my desktop and I partitioned it to drive C and drive D. If I want to copy the data from C to D, the process simply moving from C partition over to D partition. I am wondering if the SAN process in the same way which the data does not necessary need to go through the network but simply just move the data from one location to another on SAN.

Thanks
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Question by:Kinderly Wade
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Dawid Fusek earned 250 total points
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hi mate,

"My question is that if I setup raid with the hard drives on SAN and allocate the few hundred GB for couple servers will I be able to copy the data from one server to another simply as copy the data from one location of the hard drive to another?

A good example is that if I have a 1TB of hard drive on my desktop and I partitioned it to drive C and drive D. If I want to copy the data from C to D, the process simply moving from C partition over to D partition. I am wondering if the SAN process in the same way which the data does not necessary need to go through the network but simply just move the data from one location to another on SAN. "


it not exactly working like this mate. In theory this of course possible and it's normal for some advanced systems with Clusererd filesystem (like VMware VMFS or Sun ZFS and some unix and also some linux clustered FileSystems), but You probably want to "share" this LUN's (LUN is something like logical partition/disk on a disk/RAID but shared via SAN for one server or for multiple servers) to other servers which probably be a windows or linux servers without any Clustered filesystem, so then single LUN can be shared only for one server, if you do it to more than one server you start loosing data and get data corruption on that LUN because 2 servers will write to same LUN with not cluster aware filesystem and just rewrite FAT (File Allocation Table).

So easier way will be to bought/build a NAS and use a shared folders on NAS to present it to this servers and then you can easy move data on that share and use it on every server at once (if file is not using/lock for write at the same time for more than one server). NAS can be also almost as fast as SAN with some differences:
- NAS is file-level storage, SAN is block-level
- NAS storage have to be presented and pass via some network but it can be 10G Ethernet but need to share it with some protocol like CIFS/SMB, NFS or iSCSI (ir you will use iSCSI remember that iSCSI LUN even shared by NAS have to be connected to only single server, same like in SAN LUN)
- SAN storage always are presented as a LUN via protocols like FC, FCoE, iSCSI or SAS, sometimes via InfiniBand, it's a block-level access and it's always need a clustered filesystem to use single LUN on more than 1 SAN connected server
- NAS uses in most cases some kind of SW RAID that in cheap NAS are slow (if not using RAID 1/Mirror, like synology or QNAP) but sometimes with box on Solaris ZFS may be really fast but more complicated to build and configure and not always possible to buy as a BOX (for example I sell such ZFS NAS boxes based on HP, IBM, DELL or Supermicro hardware and Solaris or nexenta software but it's still not a big vendor box), but NAS may also use a good HW RAID Controllers as well
- SAN uses almast always HW RAID's, it differ between vendors but it's HW RAID with little or more BBU cache
- NAS are in most cases (cheaper solutions) single nodes with not strict hardware redundancy build-in (not more than PS) but with more expensive NAS for example based on Solaris ZFS, Open-E or DataCore SANsymphony they have full redundancy by having 2 or more Heads nodes which can be connected to single DualPort DAS or have it's own DAS attached so be a full mirror of a NAS with inline synchronization, that solution is used with most enterprice level companies for huge high availability storage
- SAN in all cases have 2 separate mirrored storage controllers in Active-Passive or Active-Active mode, their build and redundancy are much simpler than NAS redundancy config but single SAN are not fully mirrors nodes but only mirror a storage controller + PS which in 100% availability solutions still need a additional mirrored SAN with additional licenses for that mirror
- with NAS you connect it to the network (LAN) and share it resources for servers users and applications
- with SAN you connect it to server or servers and share it resources by server or servers to the users and other applications and servers


So with SAN one may ask, that is there a possibility to present one LUN for one server as a Read/Write and for rest of servers for Read-Only, unfortunately it's still not working as we expect if filesystem is not cluster aware because OS will cache FAT and not update it when it changes by another host and not see new data and changes or see bad data at all, so DON'T DO IT.

So last years NAS are so popular because they share a storage as a share via network to lot of servers and users, and SAN are going to be used mostly for Virtualization (which always use clustered filesystem) and single huge database servers or some servers share same SAN but not share same storage resources (via SAN), so not have single DAS connected to single server but have connected a SAN LUN to single server, and one SAN is used by some or lot of servers.
in general SAN's are rather faster than NAS but it depends, for example with VMware when I test the same custom build box as a SAN and as a NAS, SAN was 10-20% faster but NAS was still fast enough, even for my huge performance needs, but I have to tell that most low-end NAS like QNAP, Synology etc are much slower than any SAN on the market, this is because NAS speed depends mainly from not speed of disks and RAID controller (like it's in SAN + low latency and speed of FC) but rather from caching mechanism, local filesystem used, RAID used (cheap NAS uses sw linux raids which are slow if it's not RAID 1/Mirror), better use ZFS RAID-Z or HW RAID controllers and RAM memory for additional cache (with ZFS also SSD as a cache, sometime also used in better cheap NAS models without ZFS).
In last years SAN also starts to use little more cache (than it use defaultly on Controllers) and in few cases SSD as a cache to speedup hot IOPS requitrement and to be still little faster than NAS (with a same config but RAM) but it's not natural to SAN and in that way SAN starting to be also NAS than only a SAN, and also NAS starting to also have some features like SAN (like iSCSI and also on Solaris ZFS or some special Linux build can be a FC targets).

You also should know that Windows 2008 R2 and 2012/R2 (Enterprise and DataCenter versions only) have Clustering features and when configured can use SAN to share single SAN (LUN) between servers with Clustered Shared Volume (called by Microsoft).

So what you will use it depends what you really need and what is your budget for that and what kind of support and performance you like to achieve. Big corporations uses in 80% mostly SAN's but SMB are more using NAS than SAN and SOHO are using only NAS.

best regards
NTShad0w
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by:Gerald Connolly
Gerald Connolly earned 250 total points
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What was all that about? all that complicated answer?

The answer is yes. If you create multiple volumes on the SAN, format them and assign drive letters, say E: & F: then you can just copy stuff from C: to E: or C: to F:  or E: to F:

As far as Windows (or other OS's) is concerned they are locally connected SCSI disks and anything you can do with a physically connected SCSI disk you can do with a SAN connected Volume.
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by:Dawid Fusek
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Gerald Connolly,

My focus of a subject was mainly on that part of a question:
"My question is that if I setup raid with the hard drives on SAN and allocate the few hundred GB for couple servers will I be able to copy the data from one server to another simply as copy the data from one location of the hard drive to another? "

Which Your answer is not true (in most cases, mean without clustered filesystem), without using network he will not be able to copy the data from one server to another with LUN's connected to these servers from single SAN, so that LUN will not be shared between servers until using a clustered filesystem which is not so common (in OS'es) in my opinion to say that the answer is yes. He can of course do it on VMware ESXi with VMFS but not on normal windows disks with NTFS (when not get additional cluster aware feature).

I started with assumption that this part of question:
"A good example is that if I have a 1TB of hard drive on my desktop and I partitioned it to drive C and drive D. If I want to copy the data from C to D, the process simply moving from C partition over to D partition. I am wondering if the SAN process in the same way which the data does not necessary need to go through the network but simply just move the data from one location to another on SAN. "
...not reflecting problem at all, and your simple answer "yes" is only correct to that part of question. So this is only correct with copying data between LUNs but only within single server, not more servers what main question in my opinion ware.

So my answer is long and little complicated because the matter is little more complicated than single short answer yes or no.

Maybe let the author himself judge which answer seems to him to be more correct.
My is very descriptive but long and little complicated.
Your is very short, simple, but in my opinion rather not reflect the correct answer and for sure not describe a topic at all.

best regards
NTShad0w
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by:madunix
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Additionally, visit the following http://www.snia.org/education to get more info, to see that SAN (Storage Area Network) is a complete network, consisting of storage arrays, servers, switches, ..etc.

With implementing SAN, you could have: RAID (RAID 0, 1, 5, 6, 10), High availability, Volume management, Reliability, Data protection features, Data Replication
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by:Gerald Connolly
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David, thanks for your over long reply!

OP asked two questions, the first of which I overlooked you are correct.

So all that needed adding is a rider that said, sharing volumes between servers is not recommended without some kind of write arbitration such as provided in clustering
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by:Dawid Fusek
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I agree Gerald.

So more simple now.

1. LUN shared by SAN to more than 1 server is possible only with a clustering aware OS and FileSystem (and features enabled and configured), they are not possible to be shared between servers with normal local filesystems like NTFS or EXT without any additional Clustering software support and this is same situation like with normal hdd connected to single server, it can't be shared without a network to other server's (without special clustering software and hardware).

2. when you share a LUN from a SAN to a server it acts and looks exactly like local hdd, you may do anything with it like with normal hdd, also in theory like normal hdd you may disconnect it from one server and connect to another, do it carefully.

3. generally every storage directly connected to server (local hdd/RAID, DAS, SAN) without clustering software and feature enabled can't be shared between other servers without a network.

best regards
NTShad0w
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by:Kinderly Wade
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Thanks to Dawid and Gerald for the explaination.

Dawid is very nice to network beginner like me which he gives a lot of valuable inputs for a network beginner like me.

For Gerald the answer is short and clear which I can see the solution if I need a short answer right away.

Both of you are great! I like the answers a lot. Actually all the comments are good. I am just using the first reply from both experts as a reference to distribute the points. Thanks again experts.

For me, I will take it into consideration as in SAN vs NAS (currently I am using VMWARE for hosting all my virtual machine and this is part of the reason that I asked the question because I see an option inside VMware that allows me to share between the servers).

If I provide more requirements it will even be better for the experts to tackle my question. Here are some additional requirements:

1. currently the shared files are in separate folders on server's local drive and mapped as different drive. Users like to see them as separate partition which has different size instead of all have same size. This is why I decided to have them on different partition (in case there is a need to expand those partition I still can do so)

2. running into space issue. Current hard drive capacity is around 2TB. I need more hard drive space. This is why I am looking into SAN or NAS (I talked about SAN because I've asked around that SAN can be expansive and require more work to setup but it can be a long term solution if I need the space. There will be more database servers that I may need to set it up in the future such as a separate db servers for running reports and analyses)

3. Since SAN function the same as installing hard drives locally (I can see that if I set it up through iSCSI, it looks exactly like a local hard drive instead of a mapped network drive). This is why I asked if I have two different drives E: and F: will the SAN copy the data from E: and F: simply just moving the data from partition on the SAN to another or it will still need to go through the network.
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by:Dawid Fusek
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Good we can help mate,

Different experts have different way of answering and solving issues, and in my opinion it's good, as You observe one give you detailed point how SAN and NAS work with some examples, and second give you simple short answer, both are  ok.

For huge fast DB generally SAN (FC) is better because it have lower latency and operates directly on blocks, but it also depends of number of users and transactions, but if we compare iSCSI SAN and iSCSI NAS the differences may be as little as nothing or sometimes even NAS may be faster. Remember most NAS have such functionality like iSCSI which is a block level storage and is the same like that one iSCSI SAN have.

So for most today's home, home lab, soho and smb and mid companies - NAS is absolutely enough, especially with 10G NIC's, then you have 10G NFS and SMB/CIFS and 10G iSCSI.
If you think about SAN or NAS today, you rather have to seize your company and they needs, and expansion in nearest 5 years and budget you have, SAN protocols like FC (8G, or 16G) is cool, fast but is still little expensive and not very flexible, also SAN protocol iSCSI 10G (which also ALWAYS have every 10G NAS) is also very fast and is more flexible than FC, NFS and SMB/CIFS are NAS protocols and on 10G  they fly.

But for example if you want to create one BIG FC 8G SAN or 10G NAS and you will use only SAN protocols like FC on SAN and iSCSI on NAS... and connect to it for example 50 servers... most probably most SAN's will be faster because FC is less CPU intensive than iSCSI, but if not, so only up to maybe 20 I think NAS is a good choice (more flexible, cheaper, more cache), of course if your company is not a 5k users or more and use one huge DB.

But always you decide, heeh and "SAN or NAS" it's often last years a hard choice for everyone.

best regards
NTShad0w
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by:Gerald Connolly
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1. Shared files - you can have them on a SAN volume and share them like you do now, but if you want direct access, you will have to upgrade to a cluster so as to enable write locking for the volume. Otherwise file system and data corruption is coming your way.

2. Capacity - yes a SAN is a good way of providing extra capacity, it also means  that if you have orphaned space, ie space not used on locally attached disks that are provisioned for performance. Ie only need 500GB, but have 5x300GB 15K drives for performance

3.  Copying - there are high-end SAN systems that will do those sort of things, but in your case it will go via the server
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