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04-23-2014 03:25 AM - last edited on 04-25-2014 01:52 AM by RASHMI
04-23-2014 03:25 AM - last edited on 04-25-2014 01:52 AM by RASHMI
Hello
I'm working for a small company with approx 500 pcs. Our virtual environments storage consist of 2x HP StoreVirtual 4330 configured with Network-Raid-10 (2 way-mirror) . We are running approx 20 vms today from this storage.
We are going to extend the storage this year, and because I'm new to SAN storage (this is the only san I've admninistered) I need suggestions what is the best option for us. All equipment will be placed in the same serverrack, but this may change in the future. The extended storage will be used mainly for vms running different services, databases etc, but also for filestorage. I hope someone can answer my questions below.
The plan is to buy 2 more of the HP StoreVirtual 4330 model OR 2 HP StoreVirtual 4130
1. Are we required to buy the same model if we want so use the new nodes in the same cluster? (if we buy 4130 the disk size is different than the 4330 model).
2. Suggestions regarding Network-Raid level when we have 4-systems? (I've read that we shouldn't use Raid 5 or 6 when we use databases and so on on this storage)
3. Is the best option to add the new nodes to the same cluster or to configure a new 2-node cluster?
Thanks in advance!
Regards
Tony
P.S. This thread has been moved from Storage Area Networks (SAN) (Small and Medium Business) to HP StoreVirtual Storage / LeftHand. - Hp Forum Moderator
Solved! Go to Solution.
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04-23-2014 09:31 PM
04-23-2014 09:31 PM
Re: Extend iSCSI storage to 4 nodes
if you want to simply increase your storage size as a single block, you should buy nodes that are exactly the same as the existing ones you have and add them to the existing cluster. If you want to add its own new storage space to isolate performance, then you can get any nodes you want and add them to their own new cluster. Think of nodes like disks in a raid group... the cluster will only be as fast as the slowest node and only have as much space to contribute as the smallest node. the last thing in the world you want to do is have a cluster with 15k disks in one node and 7.2k disks in another.
You can add future nodes one at a time and have an odd number of nodes in the cluster, so unless you need to jump up two nodes right away or are getting a deal for it, you don't have to buy the nodes in pairs.
as for raid, there are two raid levels to keep in mind here, "network raid" and "HDD raid", the nodes come standard formatted with their HDDs in HDD raid5. Generally you don't need to change this and can leave it as is. If you really care about performance and don't need much space, you can convert it to Raid10, but it usually isn't needed. As for network raid, anything in production should be NR10. Avoid NR5 for anything other than static archive data (not active packups, but write once and hold forever things like your .iso CD library), and avoid NR0 for anything you care about just like you shouldn't use Raid0 for anything you care about either.
Network Raid 10 basically mirrors your data so that at all times it is stored on two nodes. The great thing about that is it allows you to reboot individual nodes and not lose data availability or really have a heart attack when any individual node has a problem. The downside is that NR10 is just like raid10 in that it takes up 2x your storage space.
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04-24-2014 10:51 PM - last edited on 04-25-2014 01:53 AM by RASHMI
04-24-2014 10:51 PM - last edited on 04-25-2014 01:53 AM by RASHMI
Re: Extend iSCSI storage to 4 nodes
Hi
Thank you for your answer. Really useful information!
I've read about Netowork-Raid levels and understand that NRaid-10 works different than "internal" raid-10 with discs.
(I thought an even number of storagenodes was required, but I understand that's just the case with RAID-10 between discs, not between storagenodes, right?)
OK, so two possibilities here I think:
1. Extend the exisiting cluster/Netowork Raid-10 to 4 nodes (I have budget to buy two)
or
2. Build a new cluster between the two new nodes
Whats the best option? As I understood this both scenarios will provide the same ammount of netto storagespace?
I mean if I extend to 4 nodes in the same cluster only one node of four can be down, but if I create a new cluster one node per cluster can become unavailable... So isn't it safer to have two clusters then?
What about performance between schenario 1 and 2?
I'm using VIP Load-balancing now when only 2-nodes, and I suppose a client will get all data from one of them, but if I have 4 nodes, will data then be read from several nodes every time then?
Do I need another FOM if i select option 2 or can the same one as in the current cluster be used for both clusters?
Thank you in advance!
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04-25-2014 11:41 AM
04-25-2014 11:41 AM
Re: Extend iSCSI storage to 4 nodes
correct, network raid 10 is not exactly the same as disk raid 10. both do a mirror+stripe scheme, but network raid is more advanced in that it will make sure your data is on two different nodes, but it doesn't have to be the same two different nodes, so if your data is "ABC", node one might hold data AB, node two might hold BC, and node three might hold AC.
As for what is better... a 4-node cluster or two 2-node clusters, the answer is "it depends". If the nodes you are planning to add are identical AND you don't require performance isolation between some of your LUNs, you are better off creating a single 4-node cluster because of a number of reasons: (1) all LUNs will benefit slightly by a performance increase by striping data across more nodes, (2) you will have one larger pool of space to split into LUNs so you can be more efficient with thin provisioning. If you are using a different model node which is faster or has a different storage capacity than your existing nodes then you need to create a seporate cluster for those nodes for the same reason you wouldn't put a 128GB SSD into a raid1 group with a 2TB 5400RPM HDD. Also, if you are really concerened that you have some LUNs that are going to require so much performance that they will negitively affect the rest of your LUNs, the only way to 100% isolate the performance is to maintian two clusters since each cluster is affectively a pool of IO+storage.
As for the FOM, it doesn't matter either way, FOMs are for maintining the managment group infrastructure and not the cluster structure. You may notice a FOM isn't a member of a cluster and you can't join it to one. You only need one FOM per management group. With four nodes, you can chose to either run four managers + one FOM, or you can run only three managers. generally the more managers the better (I think up to 5). The critical thing is you need to have an odd number of managers+FOM so there can be a clear majority to avoid a "split-brain" situation. What is better in your case would only be something you could know without more details provided. Just consider all the ways a manager could lose contact with the others and then plan for what would happen in every situation and you will be able to tell if running 5 managers (4+FOM) holds any benefit for management group availability than running 3 managers and no FOM. When planning, think about when one or multiple nodes might crash, lose power, unplug one or more NICs, have a switch die, catch fire... you name it.
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04-27-2014 06:39 AM - last edited on 04-30-2014 02:41 AM by RASHMI
04-27-2014 06:39 AM - last edited on 04-30-2014 02:41 AM by RASHMI
Re: Extend iSCSI storage to 4 nodes
Thank you again, really good explanation!
I hope this helps someone else to.
I think I will extend the current cluster to 4 nodes when the two new nodes will be of the same model.
Just a few more things I'm wondering about, I hope someone have time to answer :)
1. What happens to data if two nodes goes offline at the same time in this 4 node cluster (N Raid 10)?
I understand that data will be unavailable during the time 2 of them are down, but if lets say the reason was motherboad or power failure (something else than multiple HDD failures) will the data be available again when the two nodes are online, or is there a risk for data corruption or anything like that?
2. Network RAID 10 is fine with 4 nodes, but if I need to extend the cluster again in the future, approx when should I consider another RAID level for increased safety? (for example Network RAID 10+1)
3. I understand that the array will only use the ammount of space as the smallest node is even if there's a node with more space in the array, but lets say I need to replace theese 4 nodes in the future when they are old, is it possible then to change to another model (lager storegespace) and to just extend the usable space to the hosts when all 4 nodes has been replaced?
Reg
Tony
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04-27-2014 12:45 PM
04-27-2014 12:45 PM
Re: Extend iSCSI storage to 4 nodes
With NR10 (network raid 10) 1 node can fail in a cluster.
However in some situations 2 nodes can fail. For instance in a 4node cluster nodes 1 and 3 or 2 and 4 (odd or equal) can fail at the same time.
This is the reason, in a 2 site situation, that a site can fail while the other remains online. Here the rule is that the odd nodes must be in 1 site and the equal nodes in the other...
So in this setup it will be the same in a 10 node cluster. 5 nodes can fail, being or the odd or the equal nodes...
I will post soon (I will try this week) an indepth explanation with pictures on my blog, if you see the picture you will see it will make sense...
So NR10+1 gives you more availability. In this case 2 nodes can fail, even 1 in both sites... Buth you have less net capacity (33% instead of 50% with NR10)
Kr,
Bart
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04-28-2014 05:40 AM
04-28-2014 05:40 AM
Solution- Mark as New
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04-28-2014 11:22 AM
04-28-2014 11:22 AM
Re: Extend iSCSI storage to 4 nodes
Thank you both for your replies, I have a much better understanding of this now!
(I'm still intrested to look into the images Bart_Heungens mentioned about if/when published)
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04-29-2014 01:10 PM
04-29-2014 01:10 PM
Re: Extend iSCSI storage to 4 nodes
Hi,
There you go!
Kr,
Bart
If my post was useful, clik on my KUDOS! "White Star" !
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04-29-2014 01:32 PM
04-29-2014 01:32 PM
Re: Extend iSCSI storage to 4 nodes
nice link bart!