Re: Integration of SCST in the mainstream Linux kernel

From: david
Date: Thu Feb 07 2008 - 16:39:34 EST


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 Lang
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