Comments on: RAID 5 Stale drive detection http://www.dtidata.com/resourcecenter/2009/12/02/raid-5-stale-drive-detection/ Hard drive recovery data recovery resource center with how to guides for windows RAID Snap server file system repair NTFS partition recovery tools tips and tricks to recover data Fri, 10 Feb 2012 20:43:29 -0500 hourly 1 http://wordpress.org/?v=3.1.2 By: Richard Correa http://www.dtidata.com/resourcecenter/2009/12/02/raid-5-stale-drive-detection/comment-page-1/#comment-7864 Richard Correa Fri, 30 Jul 2010 19:19:30 +0000 http://www.dtidata.com/resourcecenter/?p=1192#comment-7864 John, When a drive drops out of a RAID 5 that drive becomes virtualized. In other words, the drive is considered there but the data written to it and read from it is calculated from the parity. That is why when you lose one drive in the array the system slows down a bit because the data read from and written to the RAID is calculated. The RAID will receive a small boost since all writes are virtual and do not take place. Parity is always written, the degraded array just virtualizes the dropped drive. If no parity was written then the RAID would become a RAID 0 and not a RAID 5. In addition, there is still rotating parity that has been written before the RAID degraded. When the dropped drive is replaced then a rebuild is done in either exclusive mode, or active mode and until the drive is rebuilt it is considered virtualized. It is always best to bring everyone off line and then do the rebuild. It is hard on the system and the card to do a rebuild while the RAID is in production. I hope I have answered your question. Regards, Richard Correa John,

When a drive drops out of a RAID 5 that drive becomes virtualized. In other words, the drive is considered there but the data written to it and read from it is calculated from the parity. That is why when you lose one drive in the array the system slows down a bit because the data read from and written to the RAID is calculated. The RAID will receive a small boost since all writes are virtual and do not take place.

Parity is always written, the degraded array just virtualizes the dropped drive. If no parity was written then the RAID would become a RAID 0 and not a RAID 5. In addition, there is still rotating parity that has been written before the RAID degraded.

When the dropped drive is replaced then a rebuild is done in either exclusive mode, or active mode and until the drive is rebuilt it is considered virtualized. It is always best to bring everyone off line and then do the rebuild. It is hard on the system and the card to do a rebuild while the RAID is in production.

I hope I have answered your question.

Regards,
Richard Correa

]]> By: John Trame http://www.dtidata.com/resourcecenter/2009/12/02/raid-5-stale-drive-detection/comment-page-1/#comment-7831 John Trame Wed, 07 Jul 2010 02:03:39 +0000 http://www.dtidata.com/resourcecenter/?p=1192#comment-7831 If a single drive fails in a raid 5 array, and that drive is not replaced for a while, I believe any new data written to the array will be written without parity. When the faulty drive is replaced, will the rebuild be able to calculate parity for the data that was written without parity? If the rebuild does calculate and record parity for the newly written data, how does it do it? Does it use information from the MFT to determine which data was written, while the array was degraded? If a single drive fails in a raid 5 array, and that drive is not replaced for a while, I believe any new data written to the array will be written without parity. When the faulty drive is replaced, will the rebuild be able to calculate parity for the data that was written without parity? If the rebuild does calculate and record parity for the newly written data, how does it do it? Does it use information from the MFT to determine which data was written, while the array was degraded?

]]> By: David http://www.dtidata.com/resourcecenter/2009/12/02/raid-5-stale-drive-detection/comment-page-1/#comment-7696 David Fri, 19 Mar 2010 13:13:46 +0000 http://www.dtidata.com/resourcecenter/?p=1192#comment-7696 Interesting write-up. I'm a technician and occasionally have to destroy individual failed drives from RAID5 arrays. Could you confirm whether it would ever be possible for anyone to recover any meaningful data from a single drive out of a RAID5, without the rest of the array? I'm interested in this from the perspective of determining what is the appropriate destruction method for the drive - no point in going to the expense of getting it granulated if there is no recoverable data on there anyway. Interesting write-up. I’m a technician and occasionally have to destroy individual failed drives from RAID5 arrays.

Could you confirm whether it would ever be possible for anyone to recover any meaningful data from a single drive out of a RAID5, without the rest of the array? I’m interested in this from the perspective of determining what is the appropriate destruction method for the drive – no point in going to the expense of getting it granulated if there is no recoverable data on there anyway.

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