[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)

To unsubscribe from this group and stop receiving emails from it, send an email to zfs-discuss+unsubscribe at zfsonlinux.org.



More information about the zfs-discuss mailing list