Category: Clustered storage

We talked with Hans O’Sullivan, CEO and Chris Farey, CTO of StorMagic during Storage Field Days 6 (SFD6, view videos of their session) a couple of weeks back and they presented some interesting technology, at least to me.

Their SvSAN, software defined storage  solution has been around since 2009, and was originally intended to provide shared storage for SMB environments but was changed in 2011 to focus more on remote offices/branch offices (ROBO) for larger customers.

What makes the SvSAN such an appealing solution is that it’s a software-only storage solution that can use a minimum of 2 servers to provide a high availability, shared block storage cluster which can all be managed from one central site. Their SvSAN installs as a virtual storage appliance that runs as a virtual machine under a hypervisor and you can assign it to manage as much or as little of the direct access or SAN attached storage available to the server.

SvSAN customers

As of last count they had 30K licenses, in 64 countries, across 6 continents, were managing over 57PB of data, and had one (large retail) customer with over 2000 sites managed from one central location.  They had pictures of one customer in their presentation which judging by the color was obvious who it was but they couldn’t actually say.

One customer with a 1000’s of sites had prior storage that was causing 100’s of store outages a year, each of which averaged 6 hours to recover which cost them $6K each. Failure cost could be much larger and much longer, if there was a data loss.  They obviously needed a much more reliable storage system and wanted to reduce their cost of maintenance. Turning to SvSAN saved them lot’s of $s and time and eliminated their maintenance downtime.

Their largest vertical is retail but StorMagic does well in most ROBO environments which have limited IT staff, and limited data requirements. Other verticals they mentioned included defense (they specifically mentioned the German Army who have a parachute deployable, all-SSD SvSAN storage/data center), manufacturing (with small remote factories), government with numerous sites around the world, financial services (banks with many remote offices), restaurant and hotel chains, large energy companies, wind farms, etc.  Hans mentioned one a large wind farm operator that said their “field” data centers were so remote it took 6 days to get someone out to them to solve a problem but they needed 600GBs of shared storage to manage the complex.

SvSAN architecture

SvSAN uses synchronous mirroring between pairs of servers so that the data is constantly available in both servers of a pair. Presumably the amount of storage available to the SvSAN VSA’s running in the two servers have to be similar in capacity and performance.

An SvSAN cluster can grow by adding pairs of servers or by adding storage to an already present SvSAN cluster. One can have as many pairs of servers in an SvSAN local cluster as you want (probably some maximum here but I can’t recall what they said). The cluster interconnect is 1GbE or 10GbE. Most (~90%) of SvSAN implementations are under 2TB of data but their largest single clustered configuration is 200TB.

SvSAN supplies iSCSI storage services and runs inside a Linux virtual machine. But SvSAN can support both bare metal as well as virtualized server environments.

All the storage within a server that is assigned to SvSAN is pooled together and carved out as iSCSI virtual disks.  SvSAN can make use of raid controller with JBODs, DAS or even SAN storage, anything that is accessible to a virtual machine can be configured as part of SvSAN’s storage pool.

Servers that are accessing the shared iSCSI storage may access either of the servers in a synchronous mirrored pair. As it’s a synchronous mirror, any writes written to one of the servers is automatically mirrored to the other side before an acknowledgement is sent back to the host. Synchronous mirroring depends on multi-pathing software at the host.

As in any solution that supports active-active read-write access there is a need for a Quorum service to be hosted somewhere in the environment. Hopefully, at some location distinct from where a problem could potentially occur, but it doesn’t have to be. In StorMagic’s case this could reside on any physical server, even in the same environment. The Quorum service is there to decide which of the two copies is “more” current when there is some sort of split brain scenario. That is when the two servers in a synchronized pair lose communication with one another. At that point the Quorum service declares one dead and the other active and from that point on all IO activity must be done through the active SvSAN server. The Quorum service can also run on Linux or Windows and remotely or locally. Any configuration changes will need to be communicated to the Quorum service.

They have a bare metal recovery solution. Specifically, when one server fails, customers can ship out another server with a matching configuration to be installed in the remote site. When the new server comes up, it auto-configures it’s storage and networking by using the currently active server in the environment and starts a resynchronization process with that server. Which all means it can be brought up into a high availability mode with almost no IT support other than what it takes to power the server and connect some networking ports. This was made for ROBO!

Code upgrades can be done by taking one of the pair of servers down and loading the new code and resynching it’s data. Then once resynch completes you can do the same with the other server.

They support a fast-resynch service for when one of the pair goes down for any reason. At that point the active server starts tracking any changes that occur in a journal and when the other server comes up it just resends the changes that have occurred since the last time it was up.

SvSAN has support for SSDs and just released an SSD write back caching feature to help improve disk write speeds. They also support an all SSD configuration for harsh environments.

StorMagic also offers an option for non-mirrored disk but I can’t imagine why anyone would use it.

They can dynamically move one mirrored iSCSI volume from one pair of servers to another, without disrupting application activity.

Minimum hardware configuration requires a single core server but can use as many cores that you can give it. StorMagic commented that a single core maxes out at 50-60K IOPS but you can always just add more cores to the solution.

The SvSAN cluster can be managed in VMware vCenter or Microsoft System Center (MSSC) and it maintains statistics which help monitor the storage clusters in the remote office environments.

They also have a scripted recipe to help bring up multiple duplicate remote sites where local staff only need to plug in minimal networking and some storage information and they are ready to go.

SvSAN pricing and other information

Their product lists for 2 servers and 2TB of data storage is $2K and they have standard license options for 4, 8, and 16TB across a server pair after which it’s unlimited amounts of storage for the same price of $10K. This doesn’t include hardware or physical data storage this is just for the SvSAN software and management.

They offer a free 60 day evaluation license on their website (see link above).

There was a lot of twitter traffic and onsite discussion as to how this compared to HP’s StorVirtual VSA solution. The contention was that StorVirtual required more nodes but there was no-one from HP there to dispute this.

Didn’t hear much about snapshot, thin provisioning, remote replication, deduplication or encryption. But for ROBO office environments, that are typically under 2TB most of these features are probably overkill, especially when there’s no permanent onsite IT staff to support the local storage environment.

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I had talked with StorMagic previously at one or more of the storage/IT conferences we have attended at the past and had relegated them to SMB  storage solutions. But after talking with them at SFD6, their solution became quite clearer. All of the sophisticated functionality they have developed together with their software only solution, seems to be  very appealing solution for these ROBO environments.