can someone explain a SAN?

[unwashed potato!]

not reallt sure how this works and i need to build a pc that connects to one already in place. do computers that connect to a SAN need a hard drive and os installed?

if so when using files on the SAN are they downloaded first, edited on the pc, saved on pc hard drive, and then put back onto the SAN when the user selects to do this?

thanks

btw this is homework but in no is this doing the homework for me, im just not sure if i need to build the pc with an os and hard drive is all.

also while here the SAN cards are super expensive, why is that? like afaik they are roughly £1200, is that correct?

 

[memyselfandi]

not reallt sure how this works and i need to build a pc that connects to one already in place. do computers that connect to a SAN need a hard drive and os installed?

if so when using files on the SAN are they downloaded first, edited on the pc, saved on pc hard drive, and then put back onto the SAN when the user selects to do this?

thanks

btw this is homework but in no is this doing the homework for me, im just not sure if i need to build the pc with an os and hard drive is all.

also while here the SAN cards are super expensive, why is that? like afaik they are roughly £1200, is that correct?

I don't support SANs but I do support Unix servers which use them.

A system using a SAN can have local disk resources as well as its SAN attached storage or it can boot off of SAN storage and run purely from the SAN, personally I prefer the former as it give you somewhere to "stand" when trying to diagnose SAN issues.

The SANs we use at work can be thought of like networks with cards and switches but instead of your usual network kit here you are talking fibre connections and switches and fibre host bus adaptors (HBAs). The SAN Support team "zone" disks from the backend storage arrays, through the switches, so that they are visible to the correct server over its HBAs.

You can think of the HBAs like SCSI cards so the disk which has been presented to them over the SAN shows up to the OS as just a disk on a controller and hence is used just as if it is local to the system. Hence you do not normally do stuff to files, save them on local disks, and then copy them onto the SAN ... you just save them to disk which happeneds to be a SAN disk. For example, if I list the disks on one of my servers it shows a list of disks, some of which are local and some are SAN ... but how I interact with them and the commands I use to do so are the same no matter if they are local or remote.

In PC terminology you could have your C: drive as a local disk but your F: drive as a disk which has actually been presented to you over the SAN and unless you actually went into the configuration and looked then someone using the box would not know this.

 

[Shaz]sigh[]

A SAN is what it says on the tin, a storage area network. It's essentially the same as a network of PCs, except you have a network of disks. Ignore the interface (be it fibre channel or ethernet), the concept is the same.

Therefore, say you're sitting on your PC connected to a SAN, any read/writes you do from that PC (to a SAN), is sent over the network and written to the disks within that SAN.

The main advantage with a SAN in an Enterprise environment (other than performance) is the fact that all your data is unified allowing the administrator to easily manage and manipulate whatever data the organisation may hold.

I can't really say it simpler than this.

There are two major interfaces used to create the network is fibre channel (FC) and iSCSI. Fibre channel is fibre (hmm!) and iSCSI is ethernet, same as you use to plug your pcs together.

From your PC, depending on your interface, you'd use a FC or iSCSI HBA (Host Bus Adapter, think network card for a SAN). The FC HBAs tend to be around £800-1000 whereas the iSCSI HBAs are sub £500. Your PC would then connect to a switch (again, think normal networking) via whichever interface chosen. The switch is connected to the SANs controller. The SAN controller can do all sort of "cool" stuff but essentially it manipulates data written to the disks within the network. From the controller, you have direct connectivity to all your disks within that SAN.

That's the basics.... regarding your question about whether your PC needs a disk/OS installed, not really. You can "Boot from SAN" whereby, when you turn your PC on, your HBA talks to the SAN, gets presented a disk and uses that disk to boot off.