Hi Tudor.

All disks I have report the same size, even though they are different
brand/model
#fdisk -l | grep Disk
Disk /dev/sdc: 2000.4 GB, 2000398934016 bytes
Disk /dev/sdd: 2000.4 GB, 2000398934016 bytes
Disk /dev/sde: 2000.4 GB, 2000398934016 bytes
Disk /dev/sdf: 2000.4 GB, 2000398934016 bytes
Disk /dev/sdg: 2000.4 GB, 2000398934016 bytes

They are 2 WD RED (WDC WD20EFRX-68AX9N0),
1 WD GREEN (WDC WD20EARX-00PASB0) and
2 SAMSUNG (HD204UI).

If the 2 WD RED bahave as they should I might buy some more as soon as
the others fail,
otherwise I will try something different (that's why I want to keep
the system as flexible as possible).

The 2 samsung SMART infos are already "screaming for help" and,
actually, a third Samsung already failed last year.
Terrible drives, terrible support from Samsung that replaced the drive
(still under warranty) with a refurbished one that failed within 10
days from arrival.

Anyway, regarding how much free space to leave, another user suggested
2-10 MB should be sufficient.

Thanks for your infos.
Andrea

On Mon, May 27, 2013 at 4:36 AM, Tudor Holton [off-list ref] wrote:

Hi Andrea,

I noticed your question wasn't answered, so I'll give it a shot. Bear in
mind that I'm relatively new here, so take everything I say with a pinch
of
salt. :-)

At some point in the past, manufacturers of hard disks released disks with
the same "marketing" size but different actual capacities.  For example,
instead of 1TB being a 1 Tebibyte 2^40 (1,099,511,627,776 bytes), they
sold
lower capacity drives by using a different base.   1TB could be 1000GB
(10^3*2^30 = 1,073,741,824,000 bytes), 1024GB (2^10*10^9 =
1,024,000,000,000
bytes) or even a "true" Terabyte at 10^12 bytes (1,000,000,000,000 bytes).
If we were swapping brands, and moved from a 2^40 to a 10^12 model, then
our
array wouldn't fit anymore. :-(

These days, things are a bit clearer as people understand the differences
between the Terabytes and Tebibytes.

Thankfully, most modern disk sizes are standardised, but still with some
small variances.  It would be wise to look at the drives you have
purchased
and look at the actual storage capacity then take the lowest one and use
that.  You may want to add in some additional buffer, also, just in case.

I hope that helps you make your decision. :-)

Cheers,
Tudor.


On 24/05/13 19:25, Andrea Bolandrina wrote:

quoted

Hi All,

In choosing the right size for a mdadm array the manual sais:
"Sometimes a replacement drive can be a little smaller than the
original drives though this should be minimised by IDEMA standards.
Such a replacement drive will be rejected by md.
To guard against this it can be useful to set the initial size
slightly smaller than the smaller device with the aim that it will
still be larger than any replacement."

I want to do a 5x2TB md (raid 6) array .
Could you advise me how "slightly smaller" should my partitions be?

100MB smaller than the actual size? 1GB?

Thank in advance for the attention.

Regards,
Andrea
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