Redundancy with a Point to Point (pt to pt) SAN
Posted on 2009-07-07
I have an old SAN that I bought to familiarize myself with the technology and configuration options outside of a production environment. (I am a network Engineer and we are in the process of moving to Blades and soon a SAN). This SAN has proved to not only be an invaluable learning tool but also much more usefulness that I had originally anticipated. I am now trying to determine the best redundancy configuration that I can put it in.
The SAN is a Infortrend IFT-6330-12. 2GB Fibre channel model, 128mb Cache Raid Controller, 12 IDE ATA Drives, Point to Point (pt to pt) topology. The SAN is populated with (12) x 200GBs drives, out of which I configured (2) x RAID 5 arrays; 6 Disks in each, giving me (2) x 1TB Volumes. I currently have the SAN connected to a Emulex LP902-DC FC 2GB HBA, connected to a Dell PowerEdge Tower Server.
It took some learning and hard trial & error but I have the unit running quite well. I used 1 array for my nightly backups and was using the other array as random storage. With the upcoming RTM release of Server 2008 R2, I have been working a lot with the R2 Beta and Hyper-V (moving VMs from Virtual Server 2005 to Hyper-V, etc). On a whim I threw a VHD on the catch all SAN array and was shocked at the performance. (ATA with a decent cached controller runs better than SATA through onboard mobo port. Who'd have thought it?)
Since then, I have been researching SAN Point to Point topology and trying to determine my options in regard to redundancy/availability. It is my understanding that from an availability standpoint, Point to Point SAN is pretty close to Direct Attached storage. Access to storage area network is dependant on the Host (Host's OS). From a configuration standpoint, I defined LDs and/or LVs, setup the Raid configuration, Mask/Map the LUNS, then configure the FC access. HBA connects to the SAN to the host. The SAN's arrays are formatted by the Host's OS. From that point on the access (reads, writes, etc) are done by or through a connect to the Host.
My issue is that I would like to use the storage on the SAN to house VHDs/VMs that will be running on machines other than the host. (I know, technically NAS, Network Storage, etc is a no-no with VMs but it can be done. Have even though of using an opensource iSCSI solution to manage the SAN arrays but that is getting off topic).
My problem boils down to if the SAN is housing data being used by multiple machines, and its host needs to reboot, gets turned off, HBA has an fault etc; it would present an issue. Ultimately I'd like to configure some redundancy to mitigate this.
Although it was my understanding that this is one of the draw backs with Pt to Pt SAN topology, I have done my homework and read about a number of scenarios that accomplish some of this. (1 Pt to Pt SAN, using multiple PIDs for each LUN, multiple HBAs, and multiple fibre switches for mirrored fibre fabric, etc). I have also read about various SAN/HBA multipath/multi-pathing solutions. Additionally I recently took the certification exams for SharePoint and read a decent amount about NLB and Clustering and wondered it that could also lend to this.
Although I believe in theory there may be a combination of these technologies that accomplish my desired out come, I haven't come across anything that covered a Point to Point configuration, with Multiple HBA's, and hosts being configured in exactly this manner.
I know my goal is reaching and before I purchase any additional components I wanted to get some feedback.