linux-kernel - Re: Integration of SCST in the mainstream Linux kernel

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Message-ID: <47AC30E8.6010205@vlnb.net>
Date:	Fri, 08 Feb 2008 13:37:28 +0300
From:	Vladislav Bolkhovitin <vst@...b.net>
To:	david@...g.hm
CC:	Bart Van Assche <bart.vanassche@...il.com>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	scst-devel@...ts.sourceforge.net,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: Integration of SCST in the mainstream Linux kernel

david@...g.hm 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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