[stgt] [PATCH 0/2] RFC - Double-linked list backing store.

[Mark Harvey]

FUJITA Tomonori wrote:
> On Mon, 18 Aug 2008 15:47:00 +1000
> Mark Harvey <markh794 at gmail.com> wrote:
> 
>> An alternative backing store primarily for SSC device which uses a meta-data header for each block of data.
>>
>> Embedded with the metadata are forward & back pointers to next & previous headers forming a double-linked list of headers.
> 
> I think that everyone agrees on having the separate metadata. When we
> discussed this last time, I thought that we use extended attributes to
> store metadata. Looks like that your code uses the first bytes of a
> file to store the metadata. Using extended attributes doesn't work?

To be honest, I haven't looked at the extended attribute method. How much data can be saved within the extended attributes ?

To support variable block, metadata needs to be kept for each block.

> 
> 
>> Patch 1/2 patch includes bs_tape and a couple of helper utilities for:
>> - creating 'blank' media
>> - Dumping media headers
>> Patch 2/2 patches the tgt-core-test script which I use to setup the VTL.
>>
>> Note: The bs_tape is almost at the same level of functionality as the bs_ssc without Richard Sharps recent patches.
> 
> Almost? What are the differences?
It does not respond correctly when hitting a filemark. Only a small amount of effort to bring up to equivalent functionality or more.

Advantage is the easy ability to implement variable size block support.

> 
> Well, I don't think that we need two ssc implementations.
True.

> We need to
> integrate two. Except for the metadata handling, what are the
> differences between them?

True. I had it within 95+% complete when Richard submitted his set of patches.

So I emailed this in as well as a comparison & comment.

Cheers
Mark
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