Re: Integration of SCST in the mainstream Linux kernel

[Vladislav Bolkhovitin]

david@xxxxxxx wrote:
> On Thu, 7 Feb 2008, Vladislav Bolkhovitin wrote:
>
> > Bart Van Assche wrote:
> >
> > > - It has been discussed which iSCSI target implementation should be in
> > > the mainstream Linux kernel. There is no agreement on this subject
> > > yet. The short-term options are as follows:
> > > 1) Do not integrate any new iSCSI target implementation in the
> > > mainstream Linux kernel.
> > > 2) Add one of the existing in-kernel iSCSI target implementations to
> > > the kernel, e.g. SCST or PyX/LIO.
> > > 3) Create a new in-kernel iSCSI target implementation that combines
> > > the advantages of the existing iSCSI kernel target implementations
> > > (iETD, STGT, SCST and PyX/LIO).
> > >
> > > As an iSCSI user, I prefer option (3). The big question is whether the
> > > various storage target authors agree with this ?
> >
> >
> > I tend to agree with some important notes:
> >
> > 1. IET should be excluded from this list, iSCSI-SCST is IET updated 
> > for SCST framework with a lot of bugfixes and improvements.
> >
> > 2. I think, everybody will agree that Linux iSCSI target should work 
> > over some standard SCSI target framework. Hence the choice gets 
> > narrower: SCST vs STGT. I don't think there's a way for a dedicated 
> > iSCSI target (i.e. PyX/LIO) in the mainline, because of a lot of code 
> > duplication. Nicholas could decide to move to either existing 
> > framework (although, frankly, I don't think there's a possibility for 
> > in-kernel iSCSI target and user space SCSI target framework) and if he 
> > decide to go with SCST, I'll be glad to offer my help and support and 
> > wouldn't care if LIO-SCST eventually replaced iSCSI-SCST. The better 
> > one should win.
>
>
> why should linux as an iSCSI target be limited to passthrough to a SCSI 
> device.
>
> the most common use of this sort of thing that I would see is to load up 
> a bunch of 1TB SATA drives in a commodity PC, run software RAID, and 
> then export the resulting volume to other servers via iSCSI. not a 
> 'real' SCSI device in sight.
>
> As far as how good a standard iSCSI is, at this point I don't think it 
> really matters. There are too many devices and manufacturers out there 
> that implement iSCSI as their storage protocol (from both sides, 
> offering storage to other systems, and using external storage). 
> Sometimes the best technology doesn't win, but Linux should be 
> interoperable with as much as possible and be ready to support the 
> winners and the loosers in technology options, for as long as anyone 
> chooses to use the old equipment (after all, we support things like 
> Arcnet networking, which lost to Ethernet many years ago)

David, your question surprises me a lot. From where have you decided 
that SCST supports only pass-through backstorage? Does the RAM disk, 
which Bart has been using for performance tests, look like a SCSI device?

SCST supports all backstorage types you can imagine and Linux kernel 
supports.

> David Lang
> -
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