Changes between Version 54 and Version 55 of FAQ


Ignore:
Timestamp:
02/25/2016 03:10:59 PM (3 years ago)
Author:
Alex Samorukov
Comment:

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  • FAQ

    v54 v55  
    195195and controller type. See our page about [wiki:Supported_RAID-Controllers smartmontools RAID controller support]
    196196for the details.
     197
     198----
     199=== What is error recovery control (ERC) and why it is important to enable it for the (S)ATA disks in RAID? ===
     200
     201
     202In computing, error recovery control (ERC) (Western Digital: time-limited error recovery (TLER), Samsung/Hitachi: command completion time limit (CCTL)) is a feature of hard disks which allow a system administrator to configure the amount of time a drive's firmware is allowed to spend recovering from a read or write error. Limiting the recovery time allows for improved error handling in hardware or software RAID environments. In some cases, there is a conflict as to whether error handling should be undertaken by the hard drive or by the RAID implementation, which leads to drives being marked as unusable and significant performance degradation, when this could otherwise have been avoided.
     203
     204It is best for ERC to be "enabled" when in a RAID array to prevent the recovery time from a disk read or write error from exceeding the RAID implementation's timeout threshold. If a drive times out, the hard disk will need to be manually re-added to the array, requiring a re-build and re-synchronization of the hard disk.
     205
     206On disks that fully implement the ATA-8 standard, the smartctl utility  can be used to control the ERC behavior of many drives by setting the SCT Error Recovery Control (scterc) parameter:
     207
     208- Reading current settings:
     209{{{
     210     
     211smartctl -l scterc /dev/sda
     212     SCT Error Recovery Control:
     213           Read: Disabled
     214          Write: Disabled
     215}}}
     216-  Changing the setting:
     217{{{
     218smartctl -l scterc,150,150 /dev/sda
     219    SCT Error Recovery Control:
     220               Read:    150 (15.0 seconds)
     221              Write:    150 (15.0 seconds)
     222}}}
     223
     224ERC control needs to be set on the boot time and if hot-replacement been made. 
    197225
    198226----