PVLinks or SecurePath ?

[Bruno Bossier_1]

I'm a bit confused on when to use PVLinks or when to use SecurePath ? I've had 3 situations :

- 1 x EV5000 + 2 HBA's to 2 SAN switches --> SecurePath, no PVLinks
- 1 x EMC + 2 HBA's to 2 SAN switches --> PowerPath + PVLinks

And now we have 2 STK's + 2 HBA's to 2 SAN switches --> SecurePath or PVLinks or anything else ?

Can anyone sched some light ?

Thanks,
Bruno

[Rainer von Bongartz]

for your EVA5000 you need SecurePath:

Different from other disk arrays like the VA or XP the two controllers A and B on an EVA are not
working active/active but rather active/passive for a LUN. That means that either Controller A
OR controller B actively serves a certain LUN, not both at the same time. Multiple LUNs of
course can be served from different controllers, so a kind of static load balancing between
both controllers is possible by distributing the LUNs across both controllers. Every controller
has 2 frontendports (FP1 and FP2) connected to fibrechannel switches. A LUN that is active
on one controller can be load balanced across these two ports.
In case of a hardware failure it may be necessary that a LUN moves from one controller to the
other controller. This controller failover needs to be initiated by the host by sending certain
SCSI commands. Most operating systems (also HPUX) are not able to send this set of SCSI
commands so additional software is needed in order to handle path failovers. For this reason
Securepath is needed in all multipath environments. Securepath also is responsible for
presenting only one path per vdisk to the host, multiple pathes are hidden

Regards
Rainer

[Bob_Vance]

With an EVA, you'll get 4 paths per LUN rather the 2 you might be used to. This is unwieldy without SP.

SP can also give you load balancing across your server HBAs, while PVlinks do not.

(( You *can* do a kind of LB manually with PVlinks, by creating multiple LUNs for a given VG rather than one large one and then making the primary path of half the LUNs out one HBA and then the other LUNs use the second HBA for primary path.
But then you have to hope that your I/O is balanced across the different LUNs. Or, further, you can manually do distributed allocation of the PEs (Physical Extents) when creating an LVOL in the VG. This effectively reduces your stripe size from being an entire LUN, to being a PE.
But you have no control over the actual load balancing across the HBAs other than hoping that your I/Os are to areas of the LUNs which are balanced over the stripes we just created.
))

bv

[Dave Hutton]

From my understanding the EVA3000 and EVA5000 can not use PVlinks and you must use securepath.

However the new up in coming EVA's 4000, 6000, 8000 you can use pvlinks or other types of software similiar to Securepath if you wanted to.

[Geoff Wild]

THis depends on your application - I can only speak of EMC - as I don't have any EV's...

Some of our Apps use Powerpath - like SAP. Another one, a POS system, had an impact with performance on Power Path - so we just use standard PVLinks on that one. That being said - even with pvlinks - we still get an impact as the failover times is too long.

Rgds...Geoff

[Bruno Bossier_1]

Thanks to all, but I'm still stuck with my question regarding my Storagetek libraries.

There are 2 STK's each with 2 SAN connection to a switch, so 4 SAN connections in total. The HP servers have each 1 SAN connection to each switch (so 2 per server).

STK talked about a tool called RDAC, but that does not exist for HP-UX. My question remains : do I need SecurePath or can I use PVLinks ? SecurePath will only show me each lun only once, whereas without SecurePath or any other multi-pathing software, each lun will be presented several times and thus you need to add all these different lun presentations to the volumegroup where LVM will recognize this as Alternate Links.

Any comments ?

Thanks,
Bruno

[Bob_Vance]

Not addressing the specifics of whether SP supports STK or not...

In general, if money were no object (last time I looked SP was fairly expensive, but I don't know the situation today), I'd certainly go with multi-pathing software. Again, you can get easy, real load balancing and, as you say, only a single device name to worry about.


tks
bv

[Uwe Zessin]

I once have been told that LUN failover on the STK arrays works similar to EVA, but Secure Path will not work with foreign storage arrays.

[Bruno Bossier_1]

I found out in the meantime that Secure Path is only required with HP storage. In our setup, we just use PVLinks. It works.

However, there is another problem. After a reboot or an ioscan, I see lots of bogus lun's all with lunid 0. The lun I need has lunid 6, but I also see lun 0 for each targetid (from 0 till 15). I already installed the latest fcd driver, but the problem remains.

Any ideas ?