Re: Split RAID: Proposal for archival RAID using incremental batch checksum

[NeilBrown <neilb@suse.de>]

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On Tue, 16 Dec 2014 21:55:15 +0530 Anshuman Aggarwal
<anshuman.aggarwal@gmail.com> wrote:

> On 2 December 2014 at 17:26, Anshuman Aggarwal
> <anshuman.aggarwal@gmail.com> wrote:
> > It works! (Atleast on a sample 5 MB device with 5 x 1MB partitions :-)
> > will find more space on my drives and do a larger test but don't see
> > why it shouldn't work)
> > Here are the following caveats (and questions):
> > - Neil, like you pointed out, the power of 2 chunk size will probably
> > need a code change (in the kernel or only in the userspace tool?)

In the kernel too.

> >     - Any performance or other reasons why a terabyte size chunk may
> > not be feasible?

Not that I can think of.

> > - Implications of safe_mode_delay
> >     - Would the metadata be updated on the block device be written to
> > and the parity device as well?

Probably.  Hard to give a specific answer to vague question.

> >     - If the drive  fails which is the same as the drive being written
> > to, would that lack of metadata updates to the other devices affect
> > reconstruction?

Again, to give a precise answer, a detailed question is needed.  Obviously
any change would have to made in such a way to ensure that things which
needed to work, did work.


> > - Adding new devices (is it possible to move the parity to the disk
> > being added? How does device addition work for RAID4 ...is it added as
> > a zero-ed out device with parity disk remaining the same)

RAID5 or RAID6 with ALGORITHM_PARITY_0 puts the parity on the early devices.
Currently if you add a device to such an array ...... I'm not sure what it
will do.  It should be possible to make it just write zeros out.


NeilBrown


> >
> >
> 
> Neil, sorry to try to bump this thread. Could you please look over the
> questions and address the points on the remaining items that can make
> it a working solution? Thanks


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