File Server - SAN or JBOD?

I have a FC SAN that is filling up quickly.  The previous storage guy put *everything* on the SAN, including the network file server storage.

I understand the value of a SAN (or I think I do) but with space at a premium, I need to understand why I shouldn't just buy some DAS and move the file server off the SAN.

Please tell me why this is a bad idea.
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RPPreacherAsked:
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exx1976Commented:
Well, I suppose that would depend on the amount of storage, the required uptime, and the number of simultaneously connected users.  Are there automated processes that are dumping data there like reporting or something?
RPPreacherAuthor Commented:
Storage: 6 TB
Uptime: 6 x 12 shop
Total users < 300, simultaneous connections < 30

The file server is just a document repository for users.
exx1976Commented:
Well, 6TB is an awful lot of storage.  To that end, imagine how painful it would be if you had to rebuild it...  Just resynching 6TB worth of RAID5 storage could take days, and that's not including putting the data back afterwards.

Generally speaking, SANs are far more redundant than are external storage cabinets, meaning less failures with the SAN, so you don't have to worry about that rebuilding.  If it DOES fail, you're going to have so much broken stuff that the last thing anyone will worry about will be the file server.

Also, look into your backup strategy.  6TB is a lot to be backing up.  At my last place, I had a fibre-attached tape library to handle all that.  You wouldn't be able to use that if you switched to local storage.

Not to mention that going through the headache of moving 6TB worth of data....  WOW!   Is storage really at THAT much of a premium?  Why not buy more SAN storage instead of DAS?

HTH,
exx
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RPPreacherAuthor Commented:
This would be RAID50 or RAID10, so the rebuild times shouldn't be too much of an issue.

Whether I back up 6 TB on a SAN or 6 TB on DAS, it's still backing up 6 TB... so I don't think that is an issue.

Moving it is a lot of work; however, I need to move it regardless.  I'm either going to purchase another SAN (ours is old) and move it to the new SAN or purchase a new SAN (for VMs, etc) and DAS (for file server).

However, the point about redundancy IS valid -- do you know of any statistical evidence pointing to failure rates on DAS vs SANs?
exx1976Commented:
Aside from the environment at my last place (all IBM gear - two EXP300 DAS cabinets and an EXP400 DAS cabinet installed along side two DS4300T SANs), no.

But it wouldn't take much to put some together.  If that's the direction you want to go with it, you shouldn't need to look any farther than the drives themselves.  FC is an enterprise-class technology in terms of speed, error correction/checking, and MTBF.  SAS and SATA and both beneath that.

If, however, you were going to get a SAN that uses SAS drives, well, then I suppose it would be 6 of one half-dozen of another.

Yes, 6TB is a lot to backup.  But, my point was that there are backup solutions out there which are capable of backing up directly off the fibre.  If you are currently doing that, then when you take that 6TB off the fibre and put it on DAS, you have two options to back it up:  Get another tape library capable of backing up that much data and attach it directly to that server, or, drag 6TB of data cross a [presumably] 1GB ethernet connection (as opposed to a 2/4/8GB FC connection).

Just something else to think about (but kind of dependent on your current backup strategy - if you already drag it all across ethernet to a DA SCSI library, then I suppose it doesn't matter).


-exx
BigSchmuhCommented:
You may consider using a Windows 2008 R2 DFS on 2 servers (on 2 different sites linked through a WAN)

You MUST estimate the documents modifications global size per day to size the WAN accordingly.

Buying 2 small (2U with 12x hotswap SATA 3.5") servers with 8x SATA 2GB in RAID10 should really be competitive against your current 6TB in a SAN...(About $5800 here)
exx1976Commented:
Pardon me for asking, but exactly how would one go about making SATA competitive against FC?  Really?  SATA is a COMPLETELY inferior technology.  The error correction is below SAS, it's single-channel/half duplex..  The list goes on.

BigSchmuhCommented:
@exx1976 : You are mixing different thinks in your rude appreciation...stay cool please

We are talking about a 6TB file-server not a 100TB 1 million simultaneous users database.

Anyway:
-Low cost high TB means you have to stay in the SATA world
-Low cost high IOPS means you although have to stay in the SATA world thanks to the SSD market
-SAS error correction is better than SATA ones : agreed for the interfaces part
-SAS channel is full duplex : agreed
-Enterprise class drives are mainly defined by their UBE/BER (Unrecoverable Bit Error/Bit Error Ratio) which is usually 1 per 10e15 in BOTH the SAS and SATA large drives world
-Most desktop class SATA are in the 1 per 10e14 range (means 8.8% probability of an error per 1 TB read ! bad idea...)
-Better UBE (1 per 10e16) exists with smaller SAS drives
-Better UBE are coming (1 per 10e17) from the SSD market
-Some SAS drives offers multipath capability through TWO SAS ports per drive thus allowing nice HA cluster...but a file-server just need some replication methods like the Win2008 R2 DFS one
-SAS drives are more expensive than SATA but offered 15krpm speed which is pointless if you are planning for SSD usage
exx1976Commented:
Everything you just posted I already know.  Don't worry, I am cool.  I'm just wondering what the basis for your statement is when you said "buying 2 small servers with 8x SATA 2[tb] in RAID10 should really be competitive against your current 6TB in a SAN"

His current SAN is Fibre Channel.  IOPS, UBE/BER, everything, it's ALL better with FC, and there isn't anything that a 7200 or even 10k SATA drive can do to challenge that.  The technology simply isn't comparable.

Further, the OP never said anything about what his budget is for this, so we don't know that it needs to be low cost.  How do we know what this 6TB of data is?  CAD/CAM renderings?  MRI images?  Who knows.  I think you're going a bit off topic is all..  The question was SAN vs. DAS.  Not SATA, not SAS, not anything like that.  But I would never, ever recommend to someone to switch from FC to SATA and tell them their performance will be the same; it's impossible.  Even first-generation 1GB 10k FC drives will run circles around the fastest crop of mechanical SATA out there today (read: not SSD).


Just my $.02.  YMMV.


-exx

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RPPreacherAuthor Commented:
I appreciate the debate.  The two posters contributed to my understanding.  I will drop the DAS idea.  Thanks!
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