Gentoo Archives: gentoo-user

From: James Broadhead <jamesbroadhead@×××××.com>
To: gentoo-user@l.g.o
Subject: Re: [gentoo-user] the same hard-drives, different number of sectors...
Date: Mon, 31 Oct 2011 09:39:28
In Reply to: Re: [gentoo-user] the same hard-drives, different number of sectors... by Mark Knecht
1 On 27 October 2011 20:35, Mark Knecht <markknecht@×××××.com> wrote:
2 > On Thu, Oct 27, 2011 at 11:41 AM, Jarry <mr.jarry@×××××.com> wrote:
3 >> Hi, perhaps someone could explain this to me:
4 >>
5 >> I have bouth two the same hard-drives. The same model
6 >> (Hitachi HUA722050CLA330), the same firmware (JP20A3EA),
7 >> the same size (500GB). Well, not exactly. Both hdparm
8 >> and fdisk report different number of sectors (976771055
9 >> versus 976773168). Although not a big difference, yet
10 >> I expected them to be exactly the same (want to use
11 >> them for raid1).
12 >>
13 >> So how is it possible they do not have the same number
14 >> of sectors? I have bought them from one supplier, even
15 >> their serial numbers are very close (only the last 2
16 >> characters out of 24 are different)...
17 >>
18 >> Jarry
19 >
20 > Maybe one has some stuff mapped out due to bad blocks found during
21 > manufacturing or something like that? Not sure what it will tell you
22 > but have you run smartctl on the drives and looked around at what they
23 > tell you to find any differences?
24 >
25 > - Mark
27 During normal operation, if a bad block is detected, that sector is
28 marked as 'bad', and a one of the free sectors (which are additional
29 to your totals) is allocated to replace it. This is called
30 Re-Allocating Sectors, and according to the Google paper[1], which
31 seems to be the only authoritative (non-marketing, non
32 industry-funded) source on hard-drive failure, re-allocated sectors
33 are indicative of impending drive failure. You can check your
34 Re-Allocated sector count using smartmontools (but I recommend that
35 you try gsmartcontrol in sunrise, which makes life easier).
37 This is made more complicated by the fact that if bad sectors (below a
38 manufacturing threshold) are detected in factory testing, they will
39 re-allocate them, and reset the SMART counter to Zero (the drive _is_
40 brand new after all!). Thus, you can buy two of the exact same model
41 of drive, and yet have different numbers of available sectors.
43 It is also possible that something entirely different is at play.
45 [1]