Boot via SAN

PowerPath will detect the failure and redirect all disk access through the other HBAs that's connected SW SAN 2.

OK,

But in this case PowerPath to Boot disk works?

Let supose, my System Operacion is up via boot disk SW SAN 1 and SPA.

If my SW SAN 1 comes down? How Does Power Path will be works?

you need to install PowerPath regardless, each HBA needs to be zoned to SPA and SPB and configured in the BIOS as well.

OK,

I understood, but I have 2 doubts.

1-) We are talking aboout (LUN) boot disk, You said that PowerPath will be redirect all connection to second HBA . In this case I am assuming that my System Operation does not coming down? The server will be avaliable to all users, 0% down time? Is that correct?

2-) Are there two kinds of PowerPath.

          a-) Free - Only redundant between HBA (1 / 2)

          b-) Payed - redundant and load balance between HBA (1 / 2).

Could I use a-) Option (free PP) only redundant ?

Thank you

Fabricio

OK Glen,

My main doubts is know how PP will be working with (Lun - Boot) case the path active becames down. Will be the server works?

Because I have to take decision about this, because the SLA of my enveriroment is high.

OK,

I understood, but I have 2 doubts.

1-) We are talking aboout (LUN) boot disk, You said that PowerPath will be redirect all connection to second HBA . In this case I am assuming that my System Operation does not coming down? The server will be avaliable to all users, 0% down time? Is that correct?

2-) Are there two kinds of PowerPath.

          a-) Free - Only redundant between HBA (1 / 2)

          b-) Payed - redundant and load balance between HBA (1 / 2).

Could I use a-) Option (free PP) only redundant ?

Thank you

Fabricio

PowerPath when installed on the host will provide fialover protestion to all the LUN's owned by the host. It does not know about boot-fron-san as PowerPath is not loaded until the OS boots. If you have one HBA in the host and two paths to the array - one to SPA and one to SPB, then if one path fails, PowerPath will failover to the surviving path. Best is to have two HBA's for best protection.

For boot-from-san, you can configure the HBA's with two paths - not sure how you do this, but this is a HBA function in the bootROM. I believe that you need two physical HBA's for this to work.

glen

When the host boots and the OS loads, PowerPath will start up. If, for example, the boot LUN (say the boot LUN is owned by SPA)  will show as the C:. If you have two paths from the HBA - one path to SPA and one path to SPB PowerPath will see that LUN on SPA and provide failover. If the on SPA path from the HBA to the LUN that is the boot LUN fails, PowerPath will switch the path to SPB. This mantains access to the LUN. If you reboot the host before the path is fixed, the HBA will not see the LUN as it is now owned by the other SP. If the HBA fails (and you have only one HBA) then you will lose all access to the LUN.

HBA1 <--> SPA0

HBA2 <--> SPB1

HBA2 <--> SPA0

HBA1 <--> SPB1

Best Practice recommends two HBAs and four paths. This requires licensed (payed) PowerPath. Basic PowerPath supports one HBA and two paths. If you received PowerPath from DELL, that version supports two HBA, but only a single path per HBA.

glen

Please allow me to clarify:

1. Boot From SAN
   
   1. This is not dependant on PowerPath.
      
   2. This is configured in the HBA settings (the options you have during the Server bootup in teh HBA configuration.  Depending on the HBA, you should be able to configure multiple paths (boot order if you will) to the LUNs for the Boot from SAN configurations.
      
2. Adding additional path
   
   1. If you do add the additional SW2 to SPB path, this will buy you the redundancy on the Switch and SP side, but you are still single point of failure (SPOF) at the HBA. 
      
   2. I would suggest that you add an additional HBA to each of your servers and patch it to your second switch.
      
   3. If you don't have a second switch, and are conecting everything through one switch; again I recommend adding the second switch or you still have SPOF at the switch chassis layer.
      
3. PowerPath
   
   1. The free version is limited, as described above.
      
   2. If you want to achieve true HA; you will need to buy the paid version -- suggest you do.
      
4. PowerPath Failover
   
   1. If you have a failure on the OS (or any other LUN) AFTER the boot from SAN operation is complete, the PowerPath will handle the immediate swap to the next avaliable path.  Again, if you have SPOF on the switch or HBA and one of those fails and kills your LUNs, PowerPath won't help you at all.
      

Hopefully that helps.

TJ

I was just about to write something about redundancy BEFORE the operating system is up and running (and PPath as well). In the BIOS of each HBA you'll have to put the boot-LUN. the controller order in the server's BIOS will now make sure the first controller with a LUN 0 will be used to boot from.

I appreciate all answers above, but my environment has the follow configuration.

1-) Server (UCS - Cisco) - 2 CNA.

2-) SW - SAN - MDS 9124

3-) Storage - CX480

Now, my System Operation is running by boot via SAN through CNA1 on  SW-SAN1 - SPA1. I can do the configuration in CNA2 on SW-SAN2 - SP2 + Zoning and from BIOS my UCS recognize the second way.

The great doubts is to know if PP will be able deal with case any device (CNA1 / SW-SAN1 / SPA1) fail, the server continues works without restart or something like that. Because that is possible to do the second way, but I need to know if will work.

Does Someone understand my problem ?

Thank you

2 HBAs with an OS up and running: you'll need a licenced PowerPath to be able to deal with path failover involving 2 HBAs.

Do this: "I can do the configuration in CNA2 on SW-SAN2 - SP2 + Zoning and from BIOS my UCS recognize the second way." and it will work fine.  PowerPath will do it's thing and you will be happy (paid version - you need the paid version).  Don't do that, and you won't be happy.