HA question

dinkohrzica

New Member
May 9, 2014
10
0
1
I wonder if I turn on HA I have now 2 servers the data is replicated 2 times... can I choose to have servers without and with HA?
If I would have Ceph then how this will work? data is replicated automatic 3 times?

Additionally what I do not get is 2 node setup on HA. I really wish to know why it is not recommended to run only 2 dedicated servers in 2 node HA?
What if I would connect 2 more dedicated servers it would be then 4 of them and quorum exists? or no? confused :)


Thanks!
 
Last edited:
I wonder if I turn on HA I have now 2 servers the data is replicated 2 times... can I choose to have servers without and with HA?

- You can have VMs in HA, but no the physical Servers in HA
- Replicate data of storages is other subject, and very useful for get HA in Storage
- Always you can choose that VMs will be in HA.

If I would have Ceph then how this will work? data is replicated automatic 3 times?

For data replicated, you can use DRBD, GlusterFS or Ceph, each one have his strengths and weaknesses, and much depends on how you configure them

Additionally what I do not get is 2 node setup on HA. I really wish to know why it is not recommended to run only 2 dedicated servers in 2 node HA?
What if I would connect 2 more dedicated servers it would be then 4 of them and quorum exists? or no? confused

Quorum is a mechanism of protection, the main idea is that two or more VMs don't have access to the same Virtual Disks in the Storage (that would be catastrophic for your data), so as each PVE Node have 1 vote, it is preferable to have a number of odd PVE nodes, or an even number of PVE nodes + a third Node with quorum disk (with iSCSI is possible). Of this manner, and with the combination of fence, never two VMs in different PVE Nodes will have access to the same Virtual Disks of the Storage.

If you have many PVE Nodes, i think that the number of PVE Nodes odd or even isn't important

Always you can have 2 PVE Nodes, with HA for your VMs + DRBD (replication of the Storage of your Virtual Disks of your VMs between PVE Nodes) + manual fence (pseudo HA, due to that a little of human intervention is required, but without lose of data of your VMs when HA is applied manually). This combination give me great satisfactions with little expense of purchase of Hardware.
 
- You can have VMs in HA, but no the physical Servers in HA
- Replicate data of storages is other subject, and very useful for get HA in Storage
- Always you can choose that VMs will be in HA.

Me: So basicly I can have VM's in and without HA. I do not understand if I have VM in HA how can I have HA in storage....you mean like ceph? If I have ceph then I do not need VM in HA? So confused :p

For data replicated, you can use DRBD, GlusterFS or Ceph, each one have his strengths and weaknesses, and much depends on how you configure them



Quorum is a mechanism of protection, the main idea is that two or more VMs don't have access to the same Virtual Disks in the Storage (that would be catastrophic for your data), so as each PVE Node have 1 vote, it is preferable to have a number of odd PVE nodes, or an even number of PVE nodes + a third Node with quorum disk (with iSCSI is possible). Of this manner, and with the combination of fence, never two VMs in different PVE Nodes will have access to the same Virtual Disks of the Storage.

If you have many PVE Nodes, i think that the number of PVE Nodes odd or even isn't important

Always you can have 2 PVE Nodes, with HA for your VMs + DRBD (replication of the Storage of your Virtual Disks of your VMs between PVE Nodes) + manual fence (pseudo HA, due to that a little of human intervention is required, but without lose of data of your VMs when HA is applied manually). This combination give me great satisfactions with little expense of purchase of Hardware.
Me: so I can have 2 dedicated servers connected together with ceph (I read that ceph requires 3 dedicated???) as HA? Deam I am confused :)

Thanks a lot
 
Me: so I can have 2 dedicated servers connected together with ceph (I read that ceph requires 3 dedicated???) as HA? Deam I am confused :)

Thanks a lot

I don't have practice with CEPH, but i know that CEPH have a poor performance versus DRBD if you want to use it with only two PVE Nodes, i know that is possible use it with only two PVE Nodes, but will be good have NICs dedicated of 10 Gb/s for the CEPH communication if you don't want have a poor performance. Here is where DRBD can shine with two dedicated NICs of 1 Gb/s with bonding "balance-rr" for get 2 Gb/s of DRBD communication (and think that DRBD only use this(these) NIC(s) for write of blocks of disk and not for the read (ie, the read is with the local disk), while CEPH is used for writes and reads, and it obviously require use more bandwith which leads to performance degradation, also CEPH have more layers into his structure and still are not optimized.

If you want to learn about of DRBD, please see these links:
1- For the firts installation in PVE: http://pve.proxmox.com/wiki/DRBD
2- For the tuning:http://www.drbd.org/users-guide-8.3/s-throughput-tuning.html
3- All for DRBD: http://www.drbd.org/users-guide-8.3/

Best regards
Cesar
 

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