[Fixed] SCSI DVD boot failure

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[Fixed] SCSI DVD boot failure

Postby Technologov » 7. Apr 2015, 21:09

Host: Win 7 x64, VBox 5.0.0-BETA1

From Version 4.3.0 changelog:
"Added SCSI CD-ROM emulation, including boot support".

I have added an emulated SCSI controller, LsiLogic (also tried BusLogic), and inserted Debian 6 DVD into it.
VM cannot boot from it. VM boots fine from emulated IDE DVD however, from same image ISO.
Attachments
Debian 6 SCSI DVD boot-2015-04-07-22-07-25.log
vbox log
(102.04 KiB) Downloaded 24 times
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Re: SCSI DVD boot failure

Postby michaln » 8. Apr 2015, 12:33

Technologov wrote:VM cannot boot from it.

How can you tell? Is there some error message?
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Re: SCSI DVD boot failure

Postby Technologov » 8. Apr 2015, 12:38

I just see that it skips over SCSI DVD, and goes to the next device.
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Re: SCSI DVD boot failure

Postby michaln » 8. Apr 2015, 12:50

And does the guest actually have the corresponding drivers? Windows 2012 R2, for example, does not. Or, is this something that worked in 4.3?

I know for a fact that for example 64-bit Ubuntu 12.04 and up or so does not have the BusLogic drivers built in, even though 32-bit Ubuntu 14.04 still does.
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Re: SCSI DVD boot failure

Postby Technologov » 8. Apr 2015, 12:55

Even if no drivers exist in guest, it should boot DVD into bootloader (isolinux), according to El-torito PC boot standard. (part of PC BIOS, and/or of SCSI controller on real PC)

UPDATE: This feature is broken in v4.3.x also.
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Re: SCSI DVD boot failure

Postby michaln » 8. Apr 2015, 14:43

OK, now I get it. The BIOS in the guest doesn't even try booting from the CD.

This is probably an old bug, and does not happen when the hard disk uses the same SCSI controller (SATA disk + SCSI CD-ROM is pretty much the definition of pointless). I'll look into it.
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Re: SCSI DVD boot failure

Postby Technologov » 8. Apr 2015, 14:54

SCSI itself not pointless ?
15-20 years ago Scuzzy was a faster version of standard IDE, so I understood the rationale. More performance + more headache for digging for custom drivers. Every SCSI is non-standard. In fact there is no standard SCSI driver, for all SCSI controllers. (unlike IDE, SATA, or USB mass storage, which have single driver)

But now?
I view Scuzzy as a non-standard version of SATA. It has similar performance (including TCQ/NCQ queues) + head-ache for digging special drivers for every SCSI controller.

Normally I don't use SCSI, but just because it was mentioned in VBox changelog, I tried to test it.

Reading manual "5.1. Hard disk controllers: IDE, SATA (AHCI), SCSI, SAS" says:
SCSI is
"Primarily for compatibility with other virtualization software, VirtualBox optionally supports LSI Logic and BusLogic SCSI controllers".
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Re: SCSI DVD boot failure

Postby michaln » 8. Apr 2015, 15:21

Technologov wrote:SCSI itself not pointless?

If you have, say, a Windows server VM from VMware installed on the LSI Logic SCSI HBA, good luck getting that going without the right emulation. But in general, for modern OSes there's little point in using SCSI emulation rather than SATA/AHCI. For older OSes which have no AHCI support the equation is different.

15-20 years ago Scuzzy was a faster version of standard IDE, so I understood the rationale.

SCSI never was such a thing, it's a generic peripheral bus used for disks, CD-ROMs, tape drives, scanners, printers, and other devices. It just happened to be used in higher end systems so the disks and controllers were typically higher performance than IDE, and things like tagged queuing or LBA addressing were implemented in SCSI years or decades before IDE (SCSI never used the antiquated C/H/S addressing that was barely adequate for floppies at all).

Every SCSI is non-standard. In fact there is no standard SCSI driver, for all SCSI controllers. (unlike IDE, SATA, or USB mass storage, which have single driver)

Very true. I think this is what killed SCSI on the desktop, the lack of a standardized HBA register interface meant that getting an OS booted/installed was always a lot more hassle. Unless one used a "pre-approved" HW/SW combination, it could be a lot of work. SAS is still alive though, and the SCSI command protocol is doing quite well in USB MSDs and iSCSI.

Normally I don't use SCSI, but just because it was mentioned in VBox changelog, I tried to test it.

None of this is new in 5.0, this was all in 4.3 already? Just wondering. Testing things is certainly good!

Anyway, the problem should be fixed in the next build. It was triggered by having a SCSI CD-ROM that wasn't preceded by any SCSI hard disk. I guess not many users managed to configure such a VM since the 4.3 release...
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