Re: Adding a smaller drive

[Bill Davidsen <davidsen@tmr.com>]

Leslie Rhorer wrote:
>>> Leslie> I may have to rethink my position on using raw drives.  If I
>>> Leslie> partition the drives, I can make the partition a bit smaller
>>> Leslie> than the whole drive, allowing for the addition of a future
>>> Leslie> drive whose size is a bit off.  I hate to waste space, but being
>>> Leslie> stuck with an undersized or limping array is worse.
>>>
>>> This is not nearly as big a problem as it used to be.  Drive
>>> manufacturers need to adhere to an IDEMA standard which requires them to
>>> use a specific LBA count for each capacity class.
>>>
>>> I.e. a 500GB Seagate drive must have exactly the same number of sectors
>>> as a 500GB Western Digital or Hitachi.
>>>
>>> The IDEMA LBA standard applies to 3.5" form factor drives over 160GB as
>>> well as 2.5" FF drives over 80 GB.
>>>       
>> Is that realy exactly so many LBA sectors or at least as many?
>>
>> I don't really see anything wrong with a 500G drive having a few more
>> sectors. And I know my Maxtor 200G disk is 3G bigger than Seagates.
>>     
>
> 	'Excellent point.  If the spec calls for a minimum of sectors, then
> it is quite possible a complaint drive might well have fewer sectors than
> the ones I used to build the array.  OTOH, all of the 1T drives on my
> systems  have precisely the same number of user available sectors, and all
> the 1.5T drives have the same number.  Since the drives represent not only
> different models from one manufacturer but also different manufacturers,
> this suggests to me an adherence to a specific spec.  On yet the other hand,
> it may merely mean they all have the same number of platters and similar
> architectures.  The 1.5T drives are less than 1.5 times bigger than the 1T
> drives, so I could not replace a 3 drive 1T triplet with a pair of 1.5T
> drives.
>   

That last sentence is important! If this is a standard, then it would 
seem to be actually intended to deceive the consumer. If there is to be 
a standard for 1, 1.5, and 2, they really should have some sensible 
relationship in size.

That said, I confess that I use partitions and leave a little breathing 
room on my drives when building a raid array.

-- 
Bill Davidsen <davidsen@tmr.com>
  Obscure bug of 2004: BASH BUFFER OVERFLOW - if bash is being run by a
normal user and is setuid root, with the "vi" line edit mode selected,
and the character set is "big5," an off-by-one error occurs during
wildcard (glob) expansion.