ProTools Nubus or PCI Disk I/O cards in multiple (PT 4/5)

[MacOS Plus]

  Something I've never been sure of is what the implications are of having multiple Disk I/O cards in one system.  Are files on each Disk I/O's SCSI bus isolated to voices on those cards, or are all files on any card's SCSI bus fully available across all cards (within TDM bandwidth limitations)?  Do the same rules apply to recording as well as playback?  I seem to recall something about ProTools automatically duplicating an audio file between drives on separate SCSI busses if you copy and paste an audio region from a track assigned to one card's voice to a different track assigned to another card's voice.  Is that true?

  What arrangement of drives and SCSI busses would give optimal performance?  Does every Disk I/O card require at least one drive attached?

[MacOS Plus]

  Now that I've gotten some additional hardware and done an extensive amount of reading, I'm going to answer my own questions.

  From what I've read, and with a few minor assumptions, each PT III Disk I/O card must host a drive on its own SCSI bus if you want the additional voices available.  If you don't do this then you also use up additional TDM bus and DSP resources getting audio to and from additional audio interface boxes attached to the other cards.  It appears the mere presence of another Disk I/O card is not enough to enable additional voices - additional drives must be present on each additional card and allocated accordingly.  PT III PCI Disk I/O cards will provide groups of voices per card as A1-16, B1-16 and C1-16 with the maximum active voice count being 48.  The virtual voice limit appears to still be 53, but use of virtual voices is extremely impractical.  The hard limit of physical simultaneous record and playback tracks would be 48 in this configuration, unless you count SampleCell card outputs also.  The minimum card arrangement to host 48 I/O worth of Audio I/O boxes would be three Disk I/O's and three Farm's because PT III cards can only host one Audio I/O box each.

  As to audio sharing between drives, if you copy regions from a track assigned on one voice group to another assigned to a different voice group, you will be prompted to have the system copy the file to the drive allocated to the second voice group and then it will play from there.  You can elect to not copy it yet and leave a "ghost" region/file which will not be playable yet.  The next time you open the session it will ask you if you want to copy the files then, after which the ghost regions/files will be playable.

  One final note - The release notes for Pro Tools 5.0.1 state that this version fixes additional voice groups with multiple PT III Disk I/O cards.  This implies that 5.0 didn't support it.  I don't yet know the situation with the 4.x series but will eventually try to confirm it.  I'll likely only be running a 4.x Nubus system though.

  My current PT III PCI hardware summary is as follows:

3 - Disk I/O
1 - Farm
1 - Farm that appears to be partly faulty
2 - SampleCell II
2 - Audio I/O box cable
1 - SCSI bus cable
2 - 5-node TDM ribbon cable
1 - 8-node TDM ribbon cable
3 - 882 I/O
2 - 888 I/O
1 - ADAT Bridge
1 - USD
1 - VSD
1 - one spare TDM module for SampleCell II card

(Some of these parts will be split between the PCI and Nubus systems.)

I am in need of at least two additional SCSI Bus cables for my PT III PCI Disk I/O cards.  If anyone can help please PM me.

[mrhappy]

Thanks for the info... I don't remember much about PT until the Mix/G4 days, even though I've been a user on some level since 'Session 8'.

[smilesdavis]

well thats exsctly what the manual says