[Asterisk-Users] TDM400P and SCSI/SATA = * noise problems???

[Damian Funnell]

Hi Tim,

Thanks for your post, it's most insightful.  It certainly puts a pretty 
large dent in my confidence in the TDM for commercial use - imagine if 
there was more than one TDM in a system (especially with a RAID adapter).

Running a PABX without hardware RAID 0 is not an option for us, as we 
don't want disk failure to result in the PABX dying, so I guess we are 
going to have to research ways of retarding it somehow.

Cheers,
D.

FFF Managed Technology Ltd
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P.O. 6368 Wellesley St
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tmassey at obscorp.com wrote:

>Yes.  It has to do with latency and bus contention.
>
>I've run a TDM board in an IBM Netfinity 5600 server with an IBM ServeRAID 
>3L controller (SCSI-U2W).  The big difference, though, is that the RAID 
>controller was on its own PCI bus, and the TDM card was on its own PCI 
>bus.
>
>With both controllers on the bus, you can have latency issues.  For 
>example, if the RAID controller sets up a DMA of a big chunk of disk, it 
>owns the bus for that transfer.  If an Ethernet packet is delayed by 50us 
>during that time, nobody cares.  But if the TDM card is delayed, it most 
>certainly cares:  especially as its generating 1000 interrupts a second!
>
>That's the problem with the TDM cards.  They do *nothing* on the CPU side. 
> The CPU has to do *everything*, and it has to do it *immediately*.  When 
>you are using plain-jane IDE, you can tweak the kernel to put the IDE 
>stuff at a low priority.  But when you've got a fancy RAID controller, it 
>tends to think it's the most important thing in the system.  And as a 
>rule, hard drive I/O usually *is* the most important I/O going on in a 
>system.  However, in this case, the TDM card trumps that.  And Digium 
>doesn't know how to tweak every last RAID driver in existence for 
>low-priority operation--or even if it's possible.  Hence, the 
>recommendation for IDE.
>Yet they require PCI 2.2, which eliminates most Pentium III's and lower! 
>:)
>
>I'm still in the midst of testing the TDM cards.  So far, so good, in an 
>EPIA-based solution and in the 5600.  But I've been through at least half 
>a dozen different systems before I've found these...
>
>Tim Massey
>
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