Seagate Archive HDD

[Xin Li]

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On 03/26/15 16:55, O'Connor, Daniel wrote:
>> On 27 Mar 2015, at 09:24, Xin Li <delphij at delphij.net> wrote: The
>> "drive managed" drives as shipped now tries to emulate normal
>> hard drive's behavior but they present unique risks: for
>> instance, a rewrite of a small block may end up in a
>> read-modify-write of a much larger area, so we must refrain from
>> doing such operations for critical file system data structure,
>> probably by reorganizing the on-disk format to satisfy the need.
> 
> I don't think this is necessarily true - I watched a very
> informative presentation about SMR drives -
> https://www.usenix.org/conference/fast15/technical-sessions/presentation/aghayev
>
>  The drive has many regions with guard bands so it doesn't have to
> rewrite the entire disk for certain writes (it may have to rewrite
> a whole band though)

That really depends on whether we can afford to lose the whole band of
(meta)data.

File systems guard against loss of critical data structure by storing
replicas of the data in distant places, but these may not have been
distant enough to survive band sized loss, or let's say loss of a few
cylinders.

That's is why I am not that optimistic about what we do nowadays, we
would need to revisit the on-disk formats with the new drives and see
if adjustments would be necessary.

Cheers,
- -- 
Xin LI <delphij at delphij.net>    https://www.delphij.net/
FreeBSD - The Power to Serve!           Live free or die
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