On Thu, 8 Mar 2012, Gerd Hoffmann wrote:
On 03/07/12 20:58, Gerhard Wiesinger wrote:
On Wed, 7 Mar 2012, Brian Jackson wrote:
I think most people trying to use qemu for anything useful have given up on if=scsi. Some distros even disable support because they don't want to QA it. That should be a decent sign that you may want to avoid it.
OK, but SAS (Serial attached SCSI) is technology in the area of storage interface technology where all big storage vendors see future (e.g. they give up: FC and SATA drives, SATA drives are replaced by MDL SATA drives (SATA 7200RPM drives with SAS interface)).
The problem isn't scsi. The problem is the lsi adapter. Problem #1 is the hardware design which makes it hard to emulate it correctly and #2 that you need a non-redistributable rom file to boot from it.
Advantages of LSI 53C895A over others: 1.) OS support is great, even for legacy systems: DOS, Win 3.1, Win95, NT 4, W2K, XP, Vista, Win7, Linux, etc. I don't know any adapter with such wide range of OS support. Also tested up to 2TB of LUNs. 2.) OS support out of the box without additional drivers for a lot of newer OSes 3.) Migration from VMWare SCSI is easy 4.) Works well here for about 1 year for legacy VMs for DOS and NT 4 5.) BIOS geometry translation is correct, also according to partition table (doesn't work correctly on MEGASAS, INT13 geometry interrupts are not correct, already reported to Hannes) 7.) LSI SCSI DMA technology is fast. I'm getting /dev/null performance over 500MB/s ..., optimized for parallel IOPS, etc. 8.) Faster ROM init than MEGASAS
Disadvantages: 1.) ROM non distributable 2.) non complete implementation 3.) 2TB limit 4.) Slower ROM INIT than without any Option ROM
Megasas also needs a ROM rom to boot from it. Not to forget iSCSI which is also current/future SCSI technology ...
Even if it is hard but I think the goal of qemu should be to implement all supported hardware pieces as good as possible (e.g. LSI 53C895A). I know it is not an easy task (see my thread about rtl8139) but I think together we can manage it.
Are there any LSI 53C895A known bugs or incomplete implementation issues which are known? Any hints on the core dump?
Therefore I don't understand why distros are giving up SAS which is also SCSI (of course old legacy SCSI is understandable).
Nobody gives up on scsi. See virtio-scsi merged recently. There also is megasas aiming for merge (which shares the boot issue with lsi though).
Disadvantage of virtio-scsi is that drivers are needed. Is INT13h supported for legacy OS and to boot? Future? But as far as I saw implemented in seabios, right? What BIOS translation is used? Buslogic? LSI logic? Partition guessing?
BTW: I've found out how LSI logic BIOS geometry translation works with (guessing) and without existing partition table. That might be an option for Seabios to implement. @Kevin: What do you think?
Ciao, Gerhard