[zfs-discuss] Clarifying questions

Michael Kjörling michael at kjorling.se
Wed Jan 8 08:44:04 EST 2014

On 8 Jan 2014 10:32 -0200, from durval.menezes at gmail.com (Durval Menezes):
> On Wed, Jan 8, 2014 at 8:59 AM, Gordan Bobic <gordan.bobic at gmail.com> wrote:
>> On Wed, Jan 8, 2014 at 10:54 AM, Durval Menezes <durval.menezes at gmail.com>wrote:
>>> I wonder what could make the media on these disks' plates so different as
>>> to be 10 times more reliable than on the "consumer" drives... or whether
>>> the manufacturers are actually lying and the error rates are about the same.
>> More ECC/sector most likely.
> In the case of 4TB drives (already at maximum density/platter *and* maximum
> number of platters per HDD with current technology),

The HGST HE6 (P/N 0F18335) seems current to me, and packs 6 TB into a
3.5" package. Using seven platters and at an almost outrageous price
tag currently, but still...

> I wonder where they are recording the extra ECC... unless they are
> reducing the number of sectors for reallocation or something...

Note that the ST4000DM000 (same 4 TB capacity, same 3.5" package, same
SATA/600 connection all as the ST4000NM0033 which I use) packs data
into 4,096 byte sectors. (It's also only rated to 2,400 power-on hours
- which is downright ridiculous IMO - whereas the STx000NM00xx are
rated to 8,760 power-on hours *per year*.) [1] Depending on the exact
ECC/FEC scheme, this may have an impact on how much ECC data is needed
to correct any given read error.

I can see the look on the face of someone who RMAs a disk that is well
within even its short warranty period for data corruption errors and
they get it back with a "sorry, it's been powered on for more than 100
days which is all we guarantee, check the data sheet" - and it's not
pretty. But really, do check the data sheet under "Reliability/Data
Integrity"; "Power-on Hours" is listed as 2,400, whereas for the
ST4000NM0033, "Power-On Hours per Year" is listed as "8760 (24×7)".
That's not a marginal difference!

[1] http://www.seagate.com/www-content/product-content/barracuda-fam/desktop-hdd/barracuda-7200-14/en-gb/docs/desktop-hdd-data-sheet-ds1770-1-1212gb.pdf

Michael Kjörling • http://michael.kjorling.semichael at kjorling.se
                “People who think they know everything really annoy
                those of us who know we don’t.” (Bjarne Stroustrup)

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