[clug] Is a weekly RAID scrub too much?

Eyal Lebedinsky eyal at eyal.emu.id.au
Fri Feb 24 11:35:59 UTC 2017

I was idly browsing when I came upon an announcement from Toshiba of a new NAS HDD family:

I took a look at the spec
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?

Does smart self-test count as data read too? I do these too...

Some modern disks record the read/write volume, take the Seagate ST4000DM000. smartctl says:
     9 Power_On_Hours          -O--CK   099   099   000    -    1059
   240 Head_Flying_Hours       ------   100   253   000    -    1038h+23m+23.410s
   241 Total_LBAs_Written      ------   100   253   000    -    23806990167
   242 Total_LBAs_Read         ------   100   253   000    -    81453441961
So about 50TB I/O, and this (4TB) disk is was used only intermittently in the RAID while I wait for
a replacement of a failed disk (44 days total). The data-sheet specifies just 55TB/year workload,
even for the larger 8TB model.

Will this data be used to deny warranty service or is this just a guideline?
Are these kind of disks simply unsuitable for RAID?

Just looking for more things to worry about :-)

Eyal Lebedinsky (eyal at eyal.emu.id.au)

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