From: Marco B. <mar...@gm...> - 2011-10-15 17:05:57
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Hi. I have a question related to reallocated sectors. if a sector that's re-allocated contained data is there possibility that the data could have been corrupted? If yes, is there any other smart parameter reporting that? Does long test indicate if the whole surface of the disk is currently readable (including the relocations that may have been performed)? So, in this case this will rule out corruption chance? Thanks in advance for your replies |
From: Alex S. <ml...@os...> - 2011-10-15 17:30:44
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On 10/15/2011 07:05 PM, Marco Barbero wrote: > Hi. > I have a question related to reallocated sectors. > if a sector that's re-allocated contained data is there possibility > that the data could have been corrupted? From WIKI: Count of reallocated sectors. When the hard drive finds a read/write/verification error, it marks that sector as "reallocated" and transfers data to a special reserved area (spare area). This process is also known as remapping, and reallocated sectors are called "remaps". The raw value normally represents a count of the bad sectors that have been found and remapped. Thus, the higher the attribute value, the more sectors the drive has had to reallocate. This allows a drive with bad sectors to continue operation; however, a drive which has had any reallocations at all is significantly more likely to fail in the near future.[2] While primarily used as a metric of the life expectancy of the drive, this number also affects performance. As the count of reallocated sectors increases, the read/write speed tends to become worse because the drive head is forced to seek to the reserved area whenever a remap is accessed. A workaround which will preserve drive speed at the expense of capacity is to create a disk partition over the region which contains remaps and instruct the operating system to not use that partition. It is possible tat reallocation could be a transparent process without any data loss, e.g. if it was failed write request. > If yes, is there any other smart parameter reporting that? Other very important parameter is "Current Pending Sector Count" (197) " Count of "unstable" sectors (waiting to be remapped, because of read errors). If an unstable sector is subsequently read successfully, this value is decreased and the sector is not remapped. Read errors on a sector will not remap the sector (since it might be readable later); instead, the drive firmware remembers that the sector needs to be remapped, and remaps it the next time it's written. > Does long test indicate if the whole surface of the disk is currently > readable (including the relocations that may have been performed)? So, > in this case this will rule out corruption chance? It depends on firmware. Of course it will not check already internal sectors which were remapped, but it will check new (reallocated) location instead. It is recommended to run long tests, especially if you had relocation or pending sectors, but of course it will not guarantee that nothing will happens with your data, so backups are still very important. |
From: Marco B. <mar...@gm...> - 2011-10-15 18:09:39
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> On 11/10/15 Alex Samorukov <ml...@os...> wrote: > It is possible tat reallocation could be a transparent process without any > data loss, e.g. if it was failed write request. According to Seagate and other vendors, 50 and more reallocated sectors are not enough to request RMA. But what worries me is the chance to have corrupted data due to reallocation and don't know a fast way to discover that. |
From: Alex S. <ml...@os...> - 2011-10-15 18:43:21
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On 10/15/2011 08:09 PM, Marco Barbero wrote: > d more reallocated > sectors are not enough to request RMA. > But what worries me is the chance to have corrupted data due to > reallocation and don't know a fast way to discover that. > The easiest way is to do something like "dd if=/dev/sda of=/dev/null bs=1m" if you are on Linux. This will read entire disk and if you will have some errors or Pending Sector Count will grow - then it is time for RMA. Anyway - reallocated sectors is something more or less typical for the desktop drives. |
From: Bruno W. I. <br...@wo...> - 2011-10-15 19:14:24
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On Sat, Oct 15, 2011 at 20:09:31 +0200, Marco Barbero <mar...@gm...> wrote: > > On 11/10/15 Alex Samorukov <ml...@os...> wrote: > > It is possible tat reallocation could be a transparent process without any > > data loss, e.g. if it was failed write request. > > According to Seagate and other vendors, 50 and more reallocated > sectors are not enough to request RMA. > But what worries me is the chance to have corrupted data due to > reallocation and don't know a fast way to discover that. If the sectors were actually reallocated they should be OK. Sectors only get reallocated if they get a good read or are written over. There is going to be some probability of a bad read being treated as good. I don't know what that typically is for disk drives, but I would expect it to be pretty low even when trying to reallocate problem sectors. |