Any disk drive from any manufacturer can exhibit sector read errors due to media defects. This is a known and accepted reality in the disk drive industry, particularly with the high recording densities employed by recent products. These media defects only affect the drive’s ability to read data from a specific sector; they do not indicate general unreliability of the disk drive. The disk drives that EMC purchases from its vendors are within specifications for soft media errors according to the vendors as well as EMC’s own Supply Base Management organization.
Prior to shipment from manufacturing, disk drives have a surface scan operation performed that detects and reallocates any sectors that are defective. This operation is run to reduce the possibility that a disk drive will experience soft media errors in operation. Improper handling after leaving EMC manufacturing can lead to the creation of additional media defects, as can improper drive handling during installation or replacement.
When a disk drive encounters trouble reading data from a sector, the drive will automatically attempt recovery of the data through its various internal methods. Whether or not the drive is eventually successful at reading the sector, the drive will report the event to FLARE. FLARE will in turn log this event as a “Soft Media Error” (event code 820) and will re-allocate the sector to a spare physical location on the drive (this does not affect the logical address of the sector). In the event that the drive was eventually successful at reading the sector, (event coded 820 with sub-code of 22), FLARE will directly write that data into the new physical location. If the correct sector data was not available, (event code 820 with sub-code of 05). There are certain tools from EMC to verify disk and check detail about these Soft Media Errors like sniffer/FBI Tool/SMART Technology etc..