Help understanding SAN technology

Posted on 2007-12-06
Last Modified: 2013-11-14
My company is relatively small but looking into getting a SAN to help manage our electronic data growth so I'm looking for some guidance.

First please clarify the following:

1. When using a SAN, I can make it so that my other windows servers "see" these hard drives and think they are directly attached to that server. i.e. it's not a shared folder that I would have to map a network drive to right?

2. Does the previous apply to virtual servers in a VMWare environment also?

3.  My SAN OS/Controller/Config allows me to allocate hard drive space to my other servers, and also allows me to increase/decrease this amount when necessary.

Secondly, any input on choosing a SAN vendor would help.  My biggest requirement is that while we don't need a lot of space today I want to have the option to grow in the future without having to purchase a lot of extra hardware (basically only want to buy additional hard drives).  I'm open to iSCSI or Fiber Channel but cost is a big factor in my decision.

Question by:mgcIT
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Accepted Solution

TheCleaner earned 200 total points
ID: 20424807
For question #1 - Yes the SAN basically can be carved out so that host servers use the SAN as if it were DASD storage on the host servers.  The clients would connect to the server as normal using mapped drives to the server.  So for instance if serverA used the SAN for shared storage, then the user would still connect to \\serverA\share.

For Question #2 - Yep

For Question #3 - It definitely should...but it depends on the type of SAN you purchase

My advice is to go with a FAS270 or similar from Netapp (IBM oems them as their N series line).  They are SANs and a NAS combined.  The benefit being that it can be its own file server as well as serving up LUNs for host servers to use (SAN part).

I've been using Netapp forever and love them...there are cheaper options out there but I still think their stuff is the best.
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Assisted Solution

Netman66 earned 150 total points
ID: 20425195
HP SANs all the way!! :o)

1)  Yes, each server will require an HBA to connect to the SAN switch.  LUNs are the setup and presented to the servers for storage.
2)  Yes, with one exception.  Using ESX, you present the storage to the ESX server, scan for it then leave it as is.  From the VM properties you can now map a RAW storage device since this space is now seen by ESX.  Again, you still need an HBA to attach to the SAN.
3)  Yes, however increasing storage space in the LUN does NOT increase the volume Windows sees.  You'll need a partition manager to increase that from within Windows.

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Author Comment

ID: 20425709
Hi - thanks for the replies.

Can you help explain what is a LUN, and what is an HBA?  Also what SAN features should I be looking at when selecting a specific vendor?  

Do you know an approx. starting price for the FAS270, as well as storage capacity (min, max)

Are there particular HPs that you like?  

Thanks again
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Assisted Solution

by:Hedley Phillips
Hedley Phillips earned 100 total points
ID: 20426393
Technically, a logical unit number or LUN is an address for an individual disk drive and by extension, the disk device itself.

Today, LUNs are normally not individual disk drives but rather virtual partitions (or volumes) of a RAID set.

Host bus adapter (HBA) connects a host system (the computer) to other network and storage devices.

Regarding SAN features, look for good redundancy, a UPS to protect the disk cache in the event of a power cut. A good control panel with good software and a way of being able to script snapshots so that you can automate the process.

We went for an Clariion AX150i (iSCSI) which is a cheap option and we find that it is not the fastest box in the rack.

To be fair, once we had gone through the initial teething problems we always have with new equipment it has been solid and is great.

Being iSCSi it can connect via normal NICs so you don't have the hassle of expensive HBA's and fibre. It has loads of capacity and is easy to use. Adding disks is easy and a doddle to create new LUNs (virtual disks) or expand existing ones.

I can create and run a snapshot on the source server, allocate it to the target server and then Rsync that data to the LUN attached to the target server all by scripted hands off commands which is great.

As it runs on ethernet, we can use standard Gigabit switches for the SAN network, again keeping costs down.
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Expert Comment

ID: 20427522
The FAS270 with about 4TB of raw storage will run around $40k.  They also have a StorageVault line for simpler configuration options and is much cheaper.

Equallogic also makes a great and easy to use SAN.
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Assisted Solution

Netman66 earned 150 total points
ID: 20427859
The only issue with iSCSI is that of bandwidth.  Since both Network traffic and Disk I/O utilizes the NIC if you have a highly utilized server (network access-wise) then you *might* end up with a traffic jam.

HBAs are not cheap, I'll admit, however they give (on average) 2GB of connection speed to the SAN for I/O.  In real terms this equates to (virtually) a directly connected disk drive - only faster.

Depending on your server make/model some SANs by the same vendors are optimized for their own equipment.  You need to make careful decisions when you buy the SAN as it's a very expensive mistake should you chose the wrong solution.

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dipersp earned 50 total points
ID: 20439321
Something else to keep in mind in terms of LUNs and performance.  I'll give a real-world example - had a client with an Exchange cluster and a SAN.  They had ONE LUN for their massive Exchange database.  Bad idea.  It's best to have a few extra LUNs allocated for performance reasons as opposed to one gigantic LUN.
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Author Closing Comment

ID: 31413294
Thanks for the help

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