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Multi-site HA with HP StoreVirtual 4000

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alfa2008
Occasional Contributor

Multi-site HA with HP StoreVirtual 4000

Hi,

 

We are about to install a system comprised by 6 HP StoreVirtual 4000 in 2 different sites. These are connected with 2 HP Blades C7000 over iSCSI, and HP Switches. All system is Windows, will run on Hyper-V 2012, and main application are Exchange, SQL, and Oracle.

 

Our idea is to make an initial syncronization locally, and then deploy equipment to a permanent site. We want if possible to install as a HA solution, creating cluster with all nodes running on Network RAID 10+2 configuration. Building are around 40 miles away from each other, and connected with 2x fibre connection with speed 30Mbps with low latency. Hourly transfer will be around 100-200 Mb.

 

My question is whether this will work on this distance with this link speed (to keep on sync all nodes), is there any risk of data corruption, if this scenario is used.

Is there a HP or whatever tool (diagnosis) to monitor transfer of data, or any backlog created?

 

Thank you

6 REPLIES
oikjn
Honored Contributor

Re: Multi-site HA with HP StoreVirtual 4000

Nice setup.  

 

First, you will need a THIRD site to house the FOM as with two sites you have no way to tell if there is a problem with the site-site link or if a site is down and so you need a thrid site for a FOM to prevent split-brain events.  You could keep this at one of your actual sites or hosted off in the cloud or at a 3rd location if you have one...  this FOM doesn't take up much bandwidth or resources in general, but its needed like a quorum disk in a traditional failover cluster.

 

 

2nd...  you can easily setup the nodes all at one site, assign them logically to the 2nd site and then move them over to the actual 2nd site after the initial sync is completed.  This is not a problem, but you want to keep in mind how you will handle the network changes... you can create a fake temp VLAN that matches the 2nd site or you can just keep them all on the same vlan and then change the nodes IP information one at a time after you move them to the new site (thats probably easier unless the 2nd site network doesn't already exist).

 

The only caution I would have with your setup is 30Mb is rather low bandwidth.  Keep in mind that for this san, you are as fast as the slowest denominator, so this means that the MAX write throughput on the cluster is going to be <30Mb since you have to write the data to each site.  Likewise, latency on your cluster writes are going to be equal to the RTT Latency of your cluster as well.  I think HP suggests 100Mb minimum, but really it just depends on the throughput you are looking for in your cluster so you might be able to get away with 30Mb or you might not.

 

Most people end up using async replication simply because of the bandwidth limitations, but if you really have fibre going between the two sites, your latency should be great at 40 miles and you just might have to reallocate bandwidth to meet whatever throughput needs you find.

Bart_Heungens
Honored Contributor

Re: Multi-site HA with HP StoreVirtual 4000

Hi,

 

Bandwidth is 1 thing, more important for me is latency... HP suggests to have a maximum latency of 2ms RTT...

 

If I remember well the rule of thumb was 50MBps per node pair... But this was mentioned in the time of Lefthand OS 9.x, never saw newer numbers more recently...

 

 

kr,

Bart

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alfa2008
Occasional Contributor

Re: Multi-site HA with HP StoreVirtual 4000

Hi,

 

Thank you for your reply.

 

Regarding bandwidth, we can go to 2x50Mbps, but for latency, we don't know because the place to move is not ready yet, so there is no way to measure, but 2ms is quite low. 

 

We have no way to have third site, but we dedicate one as primary (there is a similiar option in these storages), and failover doesn't have to be automatic, quorum will be in the first site. I checked the way these storages works in async, but I don't like these remote snapshot option, going every 30 minutes.  If it doesn't work, maybe we may have to use application replications features (Oracle, DataGuard, and SQL 2012 AlwaysOn feature), although we would like to keep with storage HA.

 

Is there any storage built-in or other tool to monitor cross-site replication, and will users notice these delay cross-site synchronization while working on applications in primary site (sorry for my ignorance).

 

Thank you

 

 

oikjn
Honored Contributor

Re: Multi-site HA with HP StoreVirtual 4000

Is it a direct fiber run between the sites or is it through some other provider where the traffice might circle the world before going to your 2nd site?  if its going direct then latency really shouldn't be an issue unless you are using really overloaded routers.

 

syncronous means the write is written to BOTH sites BEFORE a confirmation is returned to the host, so if latency it soo high, this could mean you would notice that the storage appears slow.  Not sure if you are asking to monitor if replication is happening or what your latency is, but replication is ALWAYS on, if it isn't, then you get warnings saying you have a problem with whatever node isn't replicating.  As for latency, you can monitor it in CMC at the node and LUN level for both read and write access.  At 40 miles apart, I have a hard time imagining you are going to have latency issues, but ultimately it depends on your requirements.  Some things need sub ms latency and that just isn't going to work for multi-site workloads due to this pesky thing called the laws of physics, but other things might be happy with >1sec latency... most things like ~15ms, but YMMV.  Only way to know is to test, but I wouldn't lose sleep on the latency issue unless you are consitering running some highly sensitive applications across those sites in which case you might want to see if there is another option for replication for those applications.

alfa2008
Occasional Contributor

Re: Multi-site HA with HP StoreVirtual 4000

Hi,

 

Fibre connection will be direct, and router utilization will be low, but about latency, we don't know yet. Application which will running in this system are based on SQL, and Oracle, which apart of some peak time, won't be used from than 10 users at the same time.

 

Regarding IP addressing, we want to create a logical site / subnet locally, and when moving what will change is external IP addresses of routers, which shouldn't affect local IP addresses and subneting.

 

If we decide to go on sync mode, is there any risk to have data corruption during replication to remote site due to speed, latency or other factor?

 

Thank you

oikjn
Honored Contributor
Solution

Re: Multi-site HA with HP StoreVirtual 4000

there is no additional risk of corrruption (assuming you aren't unchecking the option to wait for write confirmation in windows).  When the SAN confirms to the server that the block is written it is written to BOTH sites.  Sounds like latency won't be an issue, but you will have to test to be sure.  Since the subnet won't exist at the 2nd site until you have the SAN it does make sense to do what you described and it will work. 

 

Side note:  since you are using M$ products, make sure to use the HP DSM as that really helps a lot for the SAN performance (perticularly in a multi-site environment)  make sure to assign the server AND the nodes to the correct sites and it will further help things run smoother.