Seagate Archive HDD

[O'Connor, Daniel]

> On 27 Mar 2015, at 09:24, Xin Li <delphij at delphij.net> wrote:
> 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.

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)

It also has a log section which it writes to and then back fills into the shingled area later.

The upshot is that you get very weird latencies, but generally writing sequentially is OK. Random read is OK, random write is utterly abysmal (duh).

One thing I would like to know is if the drive supports TRIM so it can avoid rewriting a band or not.

--
Daniel O'Connor
"The nice thing about standards is that there
are so many of them to choose from."
 -- Andrew Tanenbaum
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