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<TITLE>RE: [olug] SAN Information</TITLE>
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<P><FONT SIZE=2>Bill is right for the most part, the processing we have is only the RAID controllers or the FC switch. It has it's own language and CLI that we can manage it by RS232, network or FC/AL. Some of the other controller vendors have GUIs, ours is CLI only. If I loaded Veritas volume management on the Sun it would see the LUNs and I could then create logical volumes on it and do the other stuff Bill describes. We choose not to purchase the Veritas solution. So to our Sun it is a big disk that happens to be RAID. To the NT servers it is the same, just a disk. The WWN or LUN masking keeps the different OS's from seeing each other on the FC/AL and trying to mount the disks. It is nice to consolidate storage on a FC network to make it fast and redundant, that is unless your SAN goes down. That is another topic, check out redundant SANs across geographic areas (SANs on WANs). To change RAID levels or block sizes on our unit you must reinitialize the controller via the CLI and they warn you that data may be lost. My guess is inside of Bill's box is a controller from one of the manufactures I mentioned before. There are a finite number of controller manufactures that sell the products to integrators for their systems.</FONT></P>
<P><FONT SIZE=2>I always thought of JBOD as having no RAID smarts (like a sun external disk pack) and ours is definitely not that, DigiData claims they get the most raw performance of any RAID and I know under RAID 3 using GIS type of data with large files (typically 100 meg or more) we can move data at close to 100MB/s or maximum capacity of 1GB FC/AL. They just came out with a 2GB FC model and with the new 320mb/s drives I bet you can really copy stuff fast. The Sun T3 is very close in design to Bill's Magnitude from what it sounds like. I know Sun is using a Veritas implementation on qlogic chipsets.</FONT></P>
<P><FONT SIZE=2>Changing RAID levels on the fly is a very cool feature, what I am wondering is if it really changes the physical storage blocks on disk or is it changing the blocking factors in the controller OS settings only? Most of the big smart SANs I have seen and read about really implement RAID in software and do not ever change the data on the physical disks. The algorithms used to place the block to the metal are proprietary and very specialized to their requirements and SAN OS specifics.</FONT></P>
<P><FONT SIZE=2>The mirroring can be accomplished with a snapshot group in Solaris at least. Sort of cool that you have two filesystems looking at the same inodes on disk. You can snap one and then you have a complete copy of the disk for backups or testing.</FONT></P>
<P><FONT SIZE=2>I am not familiar with RAID 5 with different parities. Can you explain that to the group? I always knew it as RAID 0-5 with some new versions like 10 and 7 coming out now. Is parity RAID changing the parity calculations or just the striping locations? When we use RAID 5 or RAID 3 it is physically changing the controller setups and the way the blocks are put to disk. Like RAID 3 only stripes parity to one disk instead of 5 as RAID 5 does.</FONT></P>
<P><FONT SIZE=2>Thanks for the thread, it has been interesting for me at least,</FONT>
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<P><FONT SIZE=2>John</FONT>
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<P><FONT SIZE=2>-----Original Message-----</FONT>
<BR><FONT SIZE=2>From: bbrush@unlnotes.unl.edu [<A HREF="mailto:bbrush@unlnotes.unl.edu">mailto:bbrush@unlnotes.unl.edu</A>]</FONT>
<BR><FONT SIZE=2>Sent: Friday, September 27, 2002 3:02 PM</FONT>
<BR><FONT SIZE=2>To: olug@olug.org</FONT>
<BR><FONT SIZE=2>Subject: RE: [olug] SAN Information</FONT>
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<P><FONT SIZE=2>This is an interesting idea, but (I think) it kind of boils down to a</FONT>
<BR><FONT SIZE=2>remote RAID attached via FC. There's no processing unit, right? While</FONT>
<BR><FONT SIZE=2>this gives you some of the benefits of a SAN appliance it doesn't give you</FONT>
<BR><FONT SIZE=2>a lot of the really useful features I've seen (at least I don't see how it</FONT>
<BR><FONT SIZE=2>does, please correct me if I'm wrong). I think this is referred to as a</FONT>
<BR><FONT SIZE=2>JBOD. (Just a bunch of disks)</FONT>
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<P><FONT SIZE=2>For instance, using the software with a Magnitude I could create a new</FONT>
<BR><FONT SIZE=2>virtual disk (vdisk) from unused space. I could then mirror it to an</FONT>
<BR><FONT SIZE=2>existing disk. Once it was mirrored I could break the mirror and I have a</FONT>
<BR><FONT SIZE=2>perfect copy of that data. I could back it up, assign it to another</FONT>
<BR><FONT SIZE=2>server, upgrade it, or do anything else I wanted to it, and my original</FONT>
<BR><FONT SIZE=2>data is unaffected, and the server OS never even knows anything about this.</FONT>
<BR><FONT SIZE=2>Let's say I make a mirror, then upgrade the mirror copy to a newer version</FONT>
<BR><FONT SIZE=2>of software and test it. If it works, I can then SWAP the two disks with</FONT>
<BR><FONT SIZE=2>my production server. If it doesn't, no biggy, delete the vdisk and start</FONT>
<BR><FONT SIZE=2>over.</FONT>
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<P><FONT SIZE=2>Oh, one thing I forgot to mention that's unique to the Xiotech Magnitude is</FONT>
<BR><FONT SIZE=2>the ability to change RAID levels on the fly. You can just select a vdisk</FONT>
<BR><FONT SIZE=2>and tell to to change from a RAID 5 to a RAID 10, or a RAID 5/parity 3 to a</FONT>
<BR><FONT SIZE=2>RAID 5/parity 9, etc.</FONT>
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<P><FONT SIZE=2>As pretty much everyone has said, it all boils down to what you need. :-)</FONT>
<BR><FONT SIZE=2>The more you need, the more money you'd better have.</FONT>
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<P><FONT SIZE=2>Bill</FONT>
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<P><FONT SIZE=2> </FONT></P>
<P><FONT SIZE=2> "Rogers, John C NWD02" </FONT></P>
<P><FONT SIZE=2> <John.C.Rogers@nwd02.usac To: "'olug@olug.org'" <olug@olug.org> </FONT></P>
<P><FONT SIZE=2> e.army.mil> cc: </FONT></P>
<P><FONT SIZE=2> Sent by: Subject: RE: [olug] SAN Information </FONT></P>
<P><FONT SIZE=2> olug-admin@olug.org </FONT></P>
<P><FONT SIZE=2> </FONT></P>
<P><FONT SIZE=2> </FONT></P>
<P><FONT SIZE=2> 09/27/2002 02:09 PM </FONT></P>
<P><FONT SIZE=2> Please respond to olug </FONT></P>
<P><FONT SIZE=2> </FONT></P>
<P><FONT SIZE=2> </FONT></P>
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<P><FONT SIZE=2>The software depends on how fancy you want to be. If you use LUN masking</FONT>
<BR><FONT SIZE=2>etc. in the controller or switch then each host can only see the LUN the</FONT>
<BR><FONT SIZE=2>controller lets it see via hardware addressing on the loop. Now some say</FONT>
<BR><FONT SIZE=2>that is not a true SAN but I use the definition that multiple hosts are</FONT>
<BR><FONT SIZE=2>using one physical disk array so I call it a SAN. Now if you add software</FONT>
<BR><FONT SIZE=2>to the mix then a whole bucket of possibilities opens up. You can choose</FONT>
<BR><FONT SIZE=2>Veritas or the software from the SAN vendor. In this case the SAN is more</FONT>
<BR><FONT SIZE=2>like another host on the loop but it's job is to store and retrieve data</FONT>
<BR><FONT SIZE=2>to/from the disks. These more advanced SANs allow you to do all sorts of</FONT>
<BR><FONT SIZE=2>cool things like have been discussed (volume management, filesystem</FONT>
<BR><FONT SIZE=2>resizing, cache stripe optimization, disk block size masking and the like).</FONT>
<BR><FONT SIZE=2>In that environment the host never really "owns" the data is how I look at</FONT>
<BR><FONT SIZE=2>it. The data belongs to the SAN and it is served to the host as it</FONT>
<BR><FONT SIZE=2>requests it.</FONT>
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<P><FONT SIZE=2>In my environment the host really owns the data because it probes the loop</FONT>
<BR><FONT SIZE=2>for the LUNs and then attaches to them and will get really mad if it does</FONT>
<BR><FONT SIZE=2>not see them (it is not a virtual volume). What is cool is that if you use</FONT>
<BR><FONT SIZE=2>fibre channel drives and fibre controllers they are all dual attached by</FONT>
<BR><FONT SIZE=2>design. So you can build a completely separate data path to the disks for</FONT>
<BR><FONT SIZE=2>redundancy if you want to. Again the more you add the more you pay. In</FONT>
<BR><FONT SIZE=2>Sun's case they have redundant interface software that watches for hardware</FONT>
<BR><FONT SIZE=2>failure and can switch to the secondary path if needed. This is basically</FONT>
<BR><FONT SIZE=2>Veritas software under the covers. The really big arrays spend a lot of</FONT>
<BR><FONT SIZE=2>effort to make them fast. Some big Hitachi units have over 10GB of disk</FONT>
<BR><FONT SIZE=2>cache (ram) that the CPU manages to allocate the writes in the most</FONT>
<BR><FONT SIZE=2>efficient manner. There is a world of difference between what I use and</FONT>
<BR><FONT SIZE=2>those units. We wanted something reasonable in cost, expandable, reliable</FONT>
<BR><FONT SIZE=2>and vendor neutral for upgrading in the future. So we built our system.</FONT>
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<P><FONT SIZE=2>John</FONT>
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<P><FONT SIZE=2>-----Original Message-----</FONT>
<BR><FONT SIZE=2>From: roger schmeits [<A HREF="mailto:schmeits@clarksoncollege.edu">mailto:schmeits@clarksoncollege.edu</A>]</FONT>
<BR><FONT SIZE=2>Sent: Friday, September 27, 2002 1:25 PM</FONT>
<BR><FONT SIZE=2>To: olug@olug.org</FONT>
<BR><FONT SIZE=2>Subject: Re: [olug] SAN Information</FONT>
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<P><FONT SIZE=2>Ok. lets say we build the SANs. Buy all the hardware ans so forth. Dont</FONT>
<BR><FONT SIZE=2>you need software to interface with the different o/s?</FONT>
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<P><FONT SIZE=2>That where it gets pricey right? I understand the hardware part but I</FONT>
<BR><FONT SIZE=2>thought there had to something in between the servers.</FONT>
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<P><FONT SIZE=2>Please correct me if I am wrong.</FONT>
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<P><FONT SIZE=2>Congrads on building your own SANs ..impressive..</FONT>
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