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SAN/Cluster choice?

Posted on 2005-04-26
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We're a small forensic engineering company, curently running W2K servers and storing our data on a 2TB SATA array we built last year.  We are thinking about providing better redundancy/100% up time for the files and have started requesting pricing on mirrored RAID5 solutions of 4-6 TB. Apple has a nice looking solution using two XServe RAID boxes connected to a dual core G5, however the G5 is still a single point of failure for accessing the data.

My own experience with clustering, well.. beyond whatever I've had to learn to pass different tests over the years I've never even touched a cluster of servers. Might anyone have thoughts on an 'entry' ( stop laughing! ) level cluster/SAN solution? I could cobble one together here by building another 2TB array( the one we built ran us $5200 a year ago including a basic W2K Server license ) and having a Windows Server mirror them but the Co President usually prefers brand name solutions with same day service, yada yada. I've been Googling about and find that the terminology on SAN vs NAS is inconsistent and that almost nobody speaks of clustering the file servers to allow for a failure there.

Any thoughts would be greatly appreciated.



                 Paul
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Question by:Bluewhale042399
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by:prof666
prof666 earned 450 total points
ID: 13869138
Do you want to cluster the application server , or cluster the storage ?

If you want to cluster the storage I would suggest something like a pair of CX500 arrays from EMC (lower models don't do cross array mirroring). They are not cheap but scale extremely well.
Alternativly there is clustering on a filer device (traditionally NAS but also iSCSI now) such as the FAS270 and upwards from NetApps. Typically SAN arrays that can do intersite mirroring tend to come
at a price premium because the sale of such functionality is key to DR/resilence infrastructures, and that never comes cheap.

What is your projected budget?? and do you have a preference of SAN vs NAS vs iSCSI??? as this will determine you price banding options.
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by:Bluewhale042399
ID: 13872686
I have a proposal to cluster/mirror the storage. I would 'like' to cluster that and the file server itself... I spoke to the apple engineer again today ( I have to laugh here: IBM wanted to bid on it, then passed our number to one of their partners, who called back an hour later and indicated that they were not interested in helping as we had 'admitted' to building our own 2TB file server... sigh. ) and he indicated they could do something with a script to copy all changes from one file server/storage unit to a separate unit, however this would not be real time.  

What I had in mind was a cluster of two file servers connected to two RAID5 arrays ( or both connected to the same mirrored array ) so that we could lose one RAID5 array or file server and still serve data up. As to budget, the Apple bid was just over $30k. We rarely use a budget, instead determine what functionality we wish and find the best solution then price for that thought.

I realize that this arena is one of the very few that still has a lot of fat for vendors to realize a profit on, but I am surprised that nobody has tried to move into the SMB market with a solution for this problem.  I  would think that most professional companies with people billing out at hundreds of dollars per hour ( thinking attys here ) would pay for such a solution..  ?

Regarding SAN vs NAS vs ISCSI... I read articles on them once in a while but have not followed the process over the past few years of determining which is which, which is best for what application, etc. I would guess that speed would not be as great a factor for us as for most simply because we have only 25 employees. We have had a number of problems over the past 1-2 years which have taken the files offline for 15 min to 4 hours once ( which doesn't include working all night two times to get the data back up by 7 am :]  ) so the case can be made for this type of solution. I just am uncertain what to call it and how to investigate the possibilities.


            Paul
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by:prof666
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If speed is not of critical performance then I would recommend a clustered NAS device for NetApps. They are not expensive compaired to SAN attached kit as you don't have the expense of buying SAN switches and HBA's. The Filers come iSCSI ready by default so you get that extra choice if you want it. 2TB can be acheived in 1 tray so expense should not breach 30K for two trays, and the software is easy enough that you should be able to make a stab at the clustering yourself is you don't wish to engage a partner.
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by:Bluewhale042399
ID: 13879893
I'll head over to Netapp.com and take a look.

Many thanks for your thoughts

    Paul
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411monk earned 600 total points
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Not to muddy your path for a decision any more than it is, but here's a couple of questions you and your organization should also be asking:

-What is your RTO?  Basically, how quickly do you need another server up and serving out data.  2 hours, 8 hours, or 24 hours?

-How much data can you lose?  Will yesterday's data be fine?  Or do you need valid data from 2 hours ago?

-Do you plan on replicating to another site?  IMHO, I don't see the value in having 2 arrays in the same site with the same data.  I make this comment assuming that your current storage solution has adequte protection level, E.g. RAID with Hot Spare ready and waiting.

If the solution requires replication (mirroring), there 2 basic methods to replicate ---- @ the array, or @ the host (server).  Server based replication is cheapest, but will steal CPU cycles from the server (this maybe minimal, dependant on your app).  Some server based replication companies are, NSI (double-take), Legato (Replistor) ..... we have done replication using Robocopy (Xcopy on steroids), however I would not recommend as a long term solution.

To help in understanding SAN vs NAS solutions, SAN solutions (Fibre Channel) work @ the block level and NAS solutions work @ the File System level.  Typical NAS protocols are CIFS (aka SMB) NFS, NTFS, etc, etc.  If you are clustering your servers, you will need disks granted @ the block level.

Here's my first suggestion, dump Apple.  This isn't there space and are not the subject matter experts on storage.  Apple makes great consumer products, but for business / enterprise solutions....walk away.  They will not be able to support whatever crazy script they create for you.

If you do not need to replicate to another site, I would go with 1 (yes just 1) rock solid, 5 nine (99.999) array.  Definitely cluster your 2 servers.  If 1 server dies, the other picks up the workload.  If a disk dies, hot spare kicks in and rebuild occurs (no impact to server).  If the array goes down, restore from tape (please do not forget tape backups, a SAN or NAS solution will never eliminate these).  With a 5 nine array, the possiblility of an antire array going down is minimized.  You will have to weigh the cost of 1 versus 2 arrays.  If you go with 2 arrays, and choose to replicate, I would look @ server based replciation such as Legato's Replistor.

One last byte before I go, if you go with a NAS solution, you can eliminate the need for the W2K servers.  My suggestion, take a look @ EMC's NS600....NAS box that can also do SAN (should you ever change direction).
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by:prof666
ID: 13885763
NS600 doesn't do SAN..only NAS. The NS600G however does do both as the NAS unit is only a gateway addon to the Clariion base. Plus the NS600G is a pairly expensive option for round 2TB considering that you must have a minimum of 5 Fibre channel disks in the DPE of the clariion (Internal falir code must sit on FC disk not SATA), and for file sharing is massivly overpowered. If you really wanted to go down the route of a clustered SAN with option to serve NAS /iSCSI then the NS500G would be cheaper (uprated NS400 model gateway). Lower models 300 etc.. don't do clustering because they only have 2 FC connections on the SP's (a dedicated 3rd is required for this function). EMC does do very good hardware but it's not the cheapest available, but you do get what you pay for in this market. I have doe close to 100 installs of Clariions and Celerra's (both NS series and CFS14's), as well as HDS, IBM and Netapps. They are all pretty much the same as hardware functionality goes, so the real questions you should be asking is about the bundled software and it's price/useability.
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by:gjohnson99
ID: 13902974
One thing you can do With iSCSI is turn drive on a local system in to a San device. Then put two such units in a cluster that would give 2 server and 2 SAN with out buying the SAN. It a full redundent system. I done this and it works.
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by:Bluewhale042399
ID: 13904860
Hi qjohnson99.  I've only read about ISCSI the past 2 years or so.  What within the ISCSI specification would allow for duplicate writes to both servers? I'm thinking about timing issues primarily.

Tks

     Paul
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by:gjohnson99
gjohnson99 earned 450 total points
ID: 13905319
What I did was setup two servers with iSCSI drive on each. iSCSI drice work with cluster. Then mirror the iSCSI drives from each server together then use that that mirrored drive as cluster shared drive. With two server you can full redundent system. Most clutser (90%) do not hare redundent shares drive systems.

I got it working with novell netware fine.

I am currently  puting together linux Cluster doing this - its looking good.

Have set up window cluster doing this, but you will neen some 3rd party sutff to make work.



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by:Bluewhale042399
ID: 13905715
Ok, thanks for the low down. I think I'm going to have to keep looking for something a little more 'turnkey'... I want it to be operable/repairable by a non techie in case I win the lottery, which means a full support warranty and our backup IT firms being able to understand it.  

Good luck with your arrays!

   Paul
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