Re: [clug] Is a weekly RAID scrub too much?

And for ZFS, the command is just that - "zpool scrub somepool"


On 26 February 2017 at 17:32, Eyal Lebedinsky <[email protected]> wrote:

> On 26/02/17 17:15, Paul Wayper wrote:
>
>> On 24/02/17 22:35, Eyal Lebedinsky wrote:
>>
>>> I was idly browsing when I came upon an announcement from Toshiba of a
>>> new NAS
>>> HDD family:
>>>     https://toshiba.semicon-storage.com/ap-en/product/storage-
>>> products/client-hdd/mn05aca-mn04acaxxx.html
>>>
>>>
>>> I took a look at the spec
>>>     https://toshiba.semicon-storage.com/content/dam/toshiba-ss/
>>> asia-pacific/docs/product/storage/product-manual/cHDD-
>>> MN05ACA_MN04ACA_Product-overview.pdf
>>>
>>> and there I see
>>>     "Rated Annual Workload (Total TB Transferred per Year, R/W)   180
>>> TB/year".
>>> and this is the same for the three models 4/6/8TB.
>>>
>>> Doing the math: a weekly scrub will read 52*8=416TB a year, more than
>>> twice
>>> the designed load.
>>> Even a monthly scrub will use up more than half the workload.
>>>
>>> Is the scrub doing more harm than good by shortening the service life of
>>> the
>>> disk?
>>>
>>
>> So, what do you mean by "weekly RAID scrub"?
>>
>> I've never heard of anyone doing this on a RAID array.
>>
>> I've used 'scrub' on a disk or files to overwrite them with random data to
>> avoid anyone using a scanning electron microscope on them to view your
>> data
>> again.  With disk geometries, cylinder tolerances, and encoding mechanisms
>> these days, even overwriting with zeros will render the data inaccessible
>> to
>> almost all attackers.
>>
>
> I use 'shred' for this.
>
> But I've never heard of 'RAID scrubbing'.  What are you doing, Eyal?
>>
>
> RAID scrub refers to, in linux software RAID, a 'check' request. It means
> that
> the full RAID is read and verified. For RAID6 it means P and Q are
> verified.
>
> You start such a check with something like:
>         # echo 'check' >/sys/block/md127/md/sync_action
> and then you can observe the progress with:
>         $ cat /proc/mdstat
> Personalities : [raid6] [raid5] [raid4]
> md127 : active raid6 sdi1[8] sde1[9] sdf1[11] sdh1[12] sdc1[0] sdg1[13]
> sdd1[10]
>       19534425600 blocks super 1.2 level 6, 512k chunk, algorithm 2 [7/7]
> [UUUUUUU]
>       [======>..............]  check = 31.7% (1241121264/3906885120)
> finish=564.2min speed=78742K/sec
>       bitmap: 1/30 pages [4KB], 65536KB chunk
>
> cheers
>
> Have fun,
>>
>> Paul
>>
>
> --
> Eyal Lebedinsky ([email protected])
>
>
> --
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> linux-w/[email protected]
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>



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