ISCSI clarification

[3DHack]

Dear Corndog and anyone else able to help,

Thanks for all your wonderfully illuminating posts, I'm learning a lot from you and the other fine folk here on SNB.

And I'm still on the search for my storage solution.

I was pretty much sold on a ZFS approach, especially when I saw that FreeNAS is now supporting it but then I saw this thread on the opensolaris forum..

http://www.opensolaris.org/jive/thread.jspa?threadID=108213&tstart=0

I read with growing horror about the known bug which exists with no recovery tools yet available.

Had to laugh when I saw you - it had to be you right? - weigh into them with a vengeance! Nice work!

So, now I'm returning to the KISS principle which I strayed rather too far from in my enthusiasm.

I'm currently set on buying two QNAP TS-410s, one for our server and the other for backup and redundancy and I'm also hoping to replicate the speed advantages that Dennis Woods had with the TS-509 and the 803.2ad switch aggregation.

http://forums.smallnetbuilder.com/showthread.php?t=463

However there is still a juicy looking piece of the storage puzzle which I hope you may be able to clarify and that it the use of ISCSI.

I have at least managed to discover that ISCSI has:

• 
  Significant speed advantages by using block level transfer, as opposed to file transfer

• 
  Each client machine is fooled (perhaps not the best way to express this), into thinking that the iscsi storage is local, as opposed to a network share, which has advantages in some situations where applications aren't able to perform cross-network tasking.

• Centralised storage is easier to administer and back up.

However, if the storage appears local to each machine, I'm not clear on how the files would then be accessible to other machines?

Am I missing the point here?

Is, as I am starting to suspect, ISCSI only for sharing the advantages and flexibility of central storage and not suited to sharing files?

Is there a way of combining the speed and backup advantages with file sharing?

To give an overview of my needs, my company does 3D animation and special effects, which involves compositing multi-layered image sequences, usually on tv commercials of 30 seconds or less. A typical job might run to 50 GB of data and 100,000 files, the smallest of which would be 50K and the largest might reach 100MB.

So We're not in the same data league as full-blown video editing but we do need pretty fast access to our image sequences and we share files regularly.

Sometimes we find we need to copy our image sequences locally to our machine when we're compositing, as the 100BaseT router/modem which is our current network, rather slows things down.

Hope this isn't too much overload, it's actually been helpful to me just writing it all down.

Cheers

3DHack

 

[corndog]

Hi 3DHack,

You are definitely onto it. iSCSI, for the most part, allows a system to access a disk or a file over the network, and use it as a local disk. Only thing - this is not generally shareable. Now, if you have the money to purchase a cluster-capable system (RedHat Enterprise Server has the GFS filesystem which is for clustering, and also the VERY expensive Windows Server Enterprise Edition has Clustering add-on for NTFS. VMWare ESX is supposed to support clustering also with its VMFS file system) then you can have multiple systems accessing the same iSCSI storage. But for "real-world" operating systems, this isn't readily available.

So, the answer is NO - you can't really share easily this way.

Aaaaaand, the most important part - while iSCSI is a protocol that is "capable" of immense speed, I'm finding that on regular user machines with regular user operating systems it is actually slower than file services. You really need an extremely high-speed-low-latency network tweaked with the eye of a SAN engineer (or at least a savvy SAN hobbyist) to really get iSCSI up to the speed of, say, NFS or the newest versions of CIFS that come with Windows 2008 Server. And with file services, you can hit those speeds with a consumer-grade switch and no tweaking.

So, from my testing, I'd recommend you go with a very fast NAS. The higher-end QNAP devices and also the bigger Netgears are your best bet in this. Might want to stay clear of the Atom-based NASes, although I'm even getting good numbers from the QNAP TS-639Pro which is Atom-based.

My 2cents anyway. Others may chime in and correct me.

Like you, I salivate and am quite enamoured by ZFS, but hmmmm I think it's still a little young to rely on for your important data (and yes that was me).

And if you want to keep your sanity, stay as far away from the DroboPro as you can. It is NOT ready for production use yet. (That's a wound I'm dealing with right now, so it's painful at the moment)

Best of luck in this. I'd suggest overall, Netgear, but you never heard that from me