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Date:      Thu, 26 Mar 2015 15:54:58 -0700
From:      Xin Li <delphij@delphij.net>
To:        Wojciech Puchar <wojtek@puchar.net>, freebsd-hackers@freebsd.org
Subject:   Re: Seagate Archive HDD
Message-ID:  <55148E42.80708@delphij.net>
In-Reply-To: <alpine.BSF.2.20.1503261124380.1417@laptop.wojtek.intra>
References:  <alpine.BSF.2.20.1503261124380.1417@laptop.wojtek.intra>

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On 03/26/15 03:26, Wojciech Puchar wrote:
> http://www.storagereview.com/seagate_archive_hdd_review_8tb
> 
> i want to buy 2 such drives for backup server.
> 
> This drives use shingled recording.
> 
> Are anyone using them and can confirm they are compatible on
> software level with other disks? I understand average random write
> time would be 5-10 times slower than normal drive because of the
> need of rewrite few full tracks worth of data, but otherwise will
> then be compatible and can i use it as usual?

My understanding is that the SMR drives are actually different class
of storage device.

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.

That's said, if the backup is mostly something where you can group
writes together and not being written often, the drives would be just
fine working with today's OS and FS because the risk is not very big
for that type of operation.

If the backup is something "warm" (i.e. a replicated database that
receives live update stream from a master one), or the power supply is
not very reliable, it's a good idea to avoid these drives for now
until we have SMR aware drivers and filesystems for the new type of
disk (and I would expect the disk used with these be host managed
ones, or we would probably need some quirks to tell the OS to avoid
doing writes in bad way).

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