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RAID data protection remains relevant

January 22, 2009 – 12:46 pm

Storage I/O trends

RAID (Redundant Array of Idle/Independent Disks) has evolved significantly since the original RAID white paper from the University of California Berkeley (Patterson, Gibson & Katz) was published 20 some years ago and in many cases is taken for granted today. There is also debate as to whether RAID is still relevant and practical given the continued increase amounts of data that needs to be protected.

RAID Examples from
Sample of some common RAID levels, general characteristics, caveat and benefits

RAID remains relevant today, granted, RAID continues to evolve as do the many variations including distributed and hybrid data protection schemes. Dave Raffo over at SearchStorage has a nice article on "The evolution of RAID data protection" with comments from me. Have a look at the Dave’s article (as well as here) along with some of the comments and thoughts from myself and others.

Ok, nuff said.

Cheers gs

Greg Schulz – Author Cloud and Virtual Data Storage Networking (CRC Press), The Green and Virtual Data Center (CRC Press) and Resilient Storage Networks (Elsevier)
twitter @storageio

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  1. 12 Responses to “RAID data protection remains relevant”

  2. Greg,

    I agree RAID is a fundamental component of data storage and isn’t going to be going away any time soon. I do question the use of the word ‘protection’ in combination with RAID. It is a small semantic issue but one that seems to confuse many, many people. While RAID does provide some ‘protection’ in regards to an actual disk failure it does not actually provide any ‘data protection’.

    The only reason I am being picky about this is because I see the effects of people believing they are being ‘protected’ by RAID in the sense that a backup would protect them recent public example being Journalspace

    While I didn’t see that one in the lab I have seen many others. I saw so many of them a while back I made a post about it myself to have a place to point IT people I run into that mis-understand what RAID is all about.

    All that said I think RAID is essential to keeping data available.

    Thanks for the post!



    By Rob McCrea on Jan 22, 2009

  3. Hello Rob and appreciate the comments.

    I would concur that RAID is more about availability or protection from device failure; however in general, it tends to get lumped in under the more generic data protection umbrella. RAID by itself is not a replacement for backup or other data protection techniques that introduce some form of a point in time consistent copy or view of the data.

    However RAID and data mirroring/replication for that matter when combined with some form of time based data protection to establish or meet and RPO, are part of an overall data availability and data protection approach.


    By Greg Schulz on Jan 22, 2009

  4. Keep in mind that latent disk errors are one of the biggest problems with RAID technology.
    If you are rebuilding a RAID, Unrecoverable Read Error (URE) can stop a RAID rebuild in its track, essentially making the entire RAID volume unusable.

    Typical ranges for hard drives are around 1 x 10^14 bits which means that 1 out of every 10^14 bits cannot be read. This means if you have 12TBs or 12x 1TB drives your probability of encountering a URE is one (i.e. it’s going to happen). If you have 2TB drives, then all you need is 6x 2TB drives and you will encounter a URE. If you have a RAID-5 group that has seven 2TB drives and one drive fails, the RAID rebuild has to read all of the remaining disks (all six of them). At that point you are almost guaranteed that during the RAID-5 rebuild, you will hit a URE and the RAID rebuild will fail. This means you have lost all of your data.

    By Ron Sunden on Jan 17, 2015

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