Topic
4 replies Latest Post - ‏2013-07-08T14:25:51Z by tuscani
tuscani
tuscani
16 Posts
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Pinned topic DDP and DS3524 Useable Space

‏2013-06-26T14:22:22Z |

Hey all.. we have a fully populated DS3524 and EXP3524 (48 x 900GB drives). All storage is a single Pool of disk. I understand this uses RADI6. When using a RAID6 calcualter it looks like I should have 40TB+ of useable space. Yet I only see 29TB in Storage Manager. Is DPP using multiple RAID6 sets and\or hot spares by default? Just trying to understand the math.. :)

 

Thanks!

 

 

Updated on 2013-06-27T14:16:50Z at 2013-06-27T14:16:50Z by tuscani
  • Tulein
    Tulein
    33 Posts
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    Re: DDP and DS3524 Useable Space

    ‏2013-07-05T15:30:34Z  in response to tuscani

    You should try using the DDP Storage Calculator (Please see the attached file). From the experience I have had, it looks to me that at the end you only get about 60% of usable storage from your original size (This is due to the fact that you will also need to leave some free space the DDP for recovery procedures, ex: Failed Drive, etc. Hope this  helps

  • Tulein
    Tulein
    33 Posts
    ACCEPTED ANSWER

    Re: DDP and DS3524 Useable Space

    ‏2013-07-05T15:38:59Z  in response to tuscani

    You should try using the DDP Storage Calculator (Please see the attached file). From the experience I have had, it looks to me that at the end you only get about 60% of usable storage from your original size (This is due to the fact that you will also need to leave some free space the DDP for recovery procedures, ex: Failed Drive, etc. Hope this  helps

  • AndersLorensen
    AndersLorensen
    139 Posts
    ACCEPTED ANSWER

    Re: DDP and DS3524 Useable Space

    ‏2013-07-05T19:48:35Z  in response to tuscani

    There is very Little information about how DDP pools Work internally. From IBM, there is litteraly none :-(

     

    The best information I've found is from Dell. The inside of the DS3524 is made by Netapp, and both IBM, Dell and other vendors makes OEM versions of it. So the info from Dell covers the DS3524 as well.

    http://i.dell.com/sites/doccontent/shared-content/data-sheets/en/Documents/Dynamic_Disk_Pooling_Technical_Report.pdf

     

    Basicly what you get inside the pool is Raid6 with 8+2 (2 Parity disks for every 8 Data disks) - so at least 20% goes to Raid Parity. Then you have your preservation, which by most is known as "hotspares" but Works a bit different. The above PDF explains that quite well actually.

    So with 48 disks, you get 10 disks that act as parity disks. Default is 4 preservation disks if I remember correctly. Left is 34 disks for data. 34 * 900 = 30,600 TB, or around 27,8 TiB (the Storage Manager reports Space in TiB, but names them wrongly TB) If you lowered the Preservation to 2 disks, you should get around the 29 TiB you mention.

     

    --

    Anders

    • tuscani
      tuscani
      16 Posts
      ACCEPTED ANSWER

      Re: DDP and DS3524 Useable Space

      ‏2013-07-08T14:25:51Z  in response to AndersLorensen

      Thanks guys.. makes sense. I was shocked by the lack of technical info out there on DDP.. lots of marketing hype of course, but not much on the technical side.