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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