RAID Data Recovery – How It Works

April 2, 2018

Diamond T recovery

RAID data recovery is probably one of the most complex processes any data recovery firm can perform. More often than not, the problems are compounded by the actions of the client prior to sending the drives in for recovery. Many users feel that it is important to try and recover the data themselves or repair the array through various system utilities, and this may be fine if the data is not critical. However, it has been our experience that when you have a RAID failure that has resolved in substantial data loss, more often than not, somebody's job is on the line if that data is not recovered. The largest piece of advise this article can provide in the event of a RAID failure: LEAVE IT ALONE.

IT professionals have a lot of pressure placed on them when a catastrophic system failure occurs. It is their job to make sure that all systems are up and running. Many times, out of panic, troubleshooting processes are initiated in order to correct the problem. Often times these processes only make a bad situation even worse, and in many instances they can render the data unrecoverable. Let's keep in mind what this data can consist of in an average corporate environment. You are probably dealing with information that cost many hundreds of thousands of dollars in labor and resources to create. Much of the data probably can not be duplicated. The intellectual value alone could have been in the many millions of dollars. Corporate executives really do not care to hear about how the failure occurred, or what unbelievable string of events led up to the server crashing. They do not care to hear the technical jargon as you try to explain to them what happened, and hope they understand that it was not your fault. They only want to know one thing … "Why was this data not backed up, and how can we get it back?"

Instead of taking chances on your own, call a data recovery professional. RAID data recovery can be expensive, but in most cases it is much less costly than trying to recreate the data that has been lost. There is a set procedure that most data recovery professionals follow when it comes to performing any recovery work. These procedures are followed and expanded upon when dealing with a RAID recovery. The first step of any RAID recovery is to make sure all of the drives are functional. In order to properly complete the recovery it is essential that all drives are fully functional (this is especially true with a RAID 0). This may involve taking any physically damaged drives into the clean room, in order to make the necessary repairs so that they function normally again. Once that is completed the next step is to make complete, sector-by-sector clones of every drive. This is not "Ghosting", but a very low-level process that allows the recovery technician to work around bad sectors, and have complete control over how the drive functions. During the cloning process, the original source drive that you sent in, is generally put in a "write protect" mode so that no data can be written to the drive. This insures that the original source data is not altered in any way.

Once the cloning process is complete, the original drives you sent in are set off to the side and are no longer touched. The actual recovery process is performed on the cloned copies, so nothing that is done during recovery can make the situation worse. After the drives are cloned, they will be loaded into an emmulator and destriped. Destriping is like taking the scattered pieces of a puzzle and putting them together neatly. Simply stated, destriping is taking the data scattered among the multiple drives that make up array and placing it onto a single destination drive. From there we have a single drive in which we can complete what we would consider to be a "normal" recovery. We can complete this process even at the multi-terrabyte level. If the damage to the stripe is not too severe, in most cases a complete rebuild of the directory structure and all associated data can be completed.

As mentioned earlier, RAID data recovery can be expensive. Depending on the company you contact the prices can vary considerably. Typically a RAID recovery can be priced anywhere from $ 800 to $ 3,000 per drive. A number of factors influence the cost, such as RAID type, file system, total size, situation of failure, etc. Many times attempt fees and assessment fees are charged if the data is unrecoverable. This is understandable due to the amount of time and resources required to perform a single RAID recovery. However, in most cases the costs involved in recovering the data are not even 1% of the data's overall value. If you are reading this article and you have not suffered a RAID failure, what are you waiting for? Back up your data NOW.

31 Comments

  • Vinayak Budapanahalli April 2, 2018 at 5:37 pm

    I have a query
    Scenario – your DB is running on archive log enabled status.

    – You have taken the back up of all files(data, spfile, control, and archive) on Mar-1 at 00:00 am to the backup location.
    then on March 4-5, you DB gets crashed along with recent archive logs(which are generated after Mar-1st).
    Can we still be able to recover the data using the archive log files which are generated after March-1 00:00 am? I mean to the most recent state of the DB along with the transaction happened on Mar-2-3-4-5 till the DB got crashed?

  • Amit Shinde April 2, 2018 at 5:37 pm

    sir,you created user but you are not connected to that user while in creating tables ,you use sys user…
    otherwise this video is very helpful for us
    thank you so much
    and add mode video with different scenario and concept…

  • Raju Bandaru April 2, 2018 at 5:37 pm

    Appreciate your awesome explanation…. 🙂

  • The Monty Channel April 2, 2018 at 5:37 pm

    In hot backup with the first scenario of data file loss,
    – You did first begin backup
    – Copy data and control file
    – Copy archive
    – Then end backup
    – Then switch achive and copied single file.

    In Hot backup with second scenario of data and control file loss,
    – You have begin backup
    – copied data and control files
    – NO Archive copied
    – End backup mode
    – Then switch achive.
    – Copied all archive logs.

    i got confused.

    Secondly, question?
    if i take backup of data control file once and then every time only archive logs, Will it be ok?

  • jq747 April 2, 2018 at 5:37 pm

    You Indian guys make the best teachers =)

  • Sufal Das April 2, 2018 at 5:37 pm

    Grate job. Carry on.

  • Onkar Kalgutkar April 2, 2018 at 5:37 pm

    do u have more videos of oracle well explained sir

  • Stanley Ismaillar April 2, 2018 at 5:37 pm

    Best User-Managed Backup on Youtube…Very well explained and good demonstration of recovering from different failure simulations.

  • Deepak Juneja April 2, 2018 at 5:37 pm

    Wonderful Really appreciated Sir

  • Ouldteyeb Naji April 2, 2018 at 5:37 pm

    Please how can i take cours online

  • yogesh negi April 2, 2018 at 5:37 pm

    we have take both datafile as well as archivelog backup and in first scenario when datafile are deleted so we only restore datafile why not archivelog file??? without recovering archive log you perform recover database.

  • sam nani April 2, 2018 at 5:37 pm

    sir how many days for linux course ?

  • veera reddy April 2, 2018 at 5:37 pm

    Please provide the some more details about RMAN backup and recovery in different server.

  • Mahesh Datta April 2, 2018 at 5:37 pm

    can u please share that ppt

  • Pravin Janjal April 2, 2018 at 5:37 pm
  • NIKUNJ SAKARIA April 2, 2018 at 5:37 pm

    This video is really Helpful..Thanks a lot…
    What command we will fire if Control Files are lost ?

  • Smart Sriram April 2, 2018 at 5:37 pm

    Great explanation, thank you very much.

  • Gulam Khan April 2, 2018 at 5:37 pm

    Hi Arun:
    Thank you for your
    great contribution. I have learnt RMAN backup,all types of recovery
    etc. by watching your tutorials. I need your help to install oracle RAC.
    Could you please send me your 2 Nodes Rac installation tutorials and
    text instruction. My Email: wticsylhet@gmail.com

  • life isgood April 2, 2018 at 5:37 pm

    hello guys , i suggest giving an overview location of oracle control files, data files, ,fast recovery area locations on disks

  • ramesh reddy April 2, 2018 at 5:37 pm

    hi iam try learn in oracle database backup and recovery iam done in session 1 & 2 but not there in session 3.please send or upload in the oracle database backup and recovry session 3. please .and advance thanku

  • Simmi Sahay April 2, 2018 at 5:37 pm

    Very well explained.

  • Sheikh Riaz April 2, 2018 at 5:37 pm

    The best,well explained video on backup and recover on the you tube.
    great job. thanks

  • Ashish Chhabra April 2, 2018 at 5:37 pm

    when you simulate recovery …start the DB without restoring file so it will show error msg… it will be good understanding….

  • Asif A April 2, 2018 at 5:37 pm

    hi, can i work as a Professional oracle DBA from this course ? r u covering everything in this training & in ur (oraclegenesis.com) website? please let me know. it would be very helpful if i we can get real life professional experience from here.

  • Stroke April 2, 2018 at 5:37 pm

    http://oraclegenesis.com/course/oracle-11g-dba/ if i take this course. where will i get the certificate. from oracle or from you? how long will this course take…?

  • Thank You April 2, 2018 at 5:37 pm

    what are the hourly, daily, weekly routine tasks/activities pertaining DB from your practical experience?
    what questions would you pose a potential DBA in the hiring process?

  • Thank You April 2, 2018 at 5:37 pm

    I'm a senior pl/sql developer so you r accomplishment in such a short period of time is unheard of.E-mail is amant4@hotmail.com. I could only imagine you've a busy schedule, but are the follow-up sessions to this such as:RMAN, DB tuning(monitoring, diagnostic, tuning), ASM , setting-RAC, e.t.c

  • Thank You April 2, 2018 at 5:37 pm

    Hi Arun!
    Your teaching technic is excellent and very motivating. You're very detailed, in the way you put yourself in the students shoes first, which other teachers lack. I'll be interested to attend your website design classes. Is there one we can attend, pls let me know. Many Tnx!

  • SYED AYAZ Ahmed April 2, 2018 at 5:37 pm

    Greetings…
    I have being learning ORACLE SQL, PL/SQL from your videos posted on youtube.com I really appreciate your effort in imparting your knowledge to us.
    I request your to please send/email the Oracle SQL,PL/SQL  scripts, PPT and notes used in the videos to “ syed15ayaz@gmail.com
    I Once again appreciate your efforts in sharing the your knowledge
    Anticipating your response earliest

  • Vijay Kumar April 2, 2018 at 5:37 pm

    can you upload the basics of sga,pga,log files,contolfiles,tablespaces and datafiles.

  • vinisha mathur April 2, 2018 at 5:37 pm

    Hey Arun You explain all the things very properly, Thank u so much .

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