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7 Replies Latest reply: Dec 22, 2012 11:29 PM by LaserSoft RSS

tablespace on flash cache

895567 Newbie
Currently Being Moderated
Hello Experts,

can i create a tablespace in exadata flash cache? if yes what is the impact?
do i need to consider flash cache as memory extension or storage extension?
  • 1. Re: tablespace on flash cache
    user296828 Expert
    Currently Being Moderated
    can i create a tablespace in exadata flash cache? if yes what is the impact?
    Yes, you can create Grid Disks based on flash memory. These flash disks can be used to configure high performance ASM disk groups to house your tablespace.

    impact, you do not loose anything but get high perfomance.
    do i need to consider flash cache as memory extension or storage extension?
    they are extension to memory but you can also use them as a permanent storage as detailed above.
  • 2. Re: tablespace on flash cache
    user296828 Expert
    Currently Being Moderated
    can i create a tablespace in exadata flash cache? if yes what is the impact?
    Yes, you can create Grid Disks based on flash memory. These flash disks can be used to configure high performance ASM disk groups to house your tablespace.

    impact, you do not loose anything but get high perfomance.
    do i need to consider flash cache as memory extension or storage extension?
    they are extension to memory but you can also use them as a permanent storage as detailed above.
  • 3. Re: tablespace on flash cache
    UweHesse Expert
    Currently Being Moderated
    Yes, that is possible. See here for an example:
    http://uhesse.com/2011/02/02/exadata-part-iv-flash-cache/

    It is questionable, though, whether that is actually required.

    Usually, the default setup, allocating the whole flash storage for the Flash Cache is appropriate.
    Also, with the advent of the write-back flash cache functionality, the sensible use cases for creating diskgroups out of flash storage should decrease even more.

    Kind regards
    Uwe Hesse

    "Don't believe it, test it!"
    http://uhesse.com
  • 4. Re: tablespace on flash cache
    933318 Newbie
    Currently Being Moderated
    1. Drop the flash cache.
    2. Create flash based Grid disk.
    3. For the remainig space in flash mememory create flash cache.
    4. Create the Tablespace using this diskgroup.

    Things to consider.
    1. The peformance of the data stored is better, ideal to use some thing like plan table in DW envs or frequently accessed data.
    2. Risk is invloved with loosing the data, as the flash memory is unstable.


    Here is a bit invotive way how you can achive both. I have not tested this but may be you can try.

    1. Storage server1, drop flash cache and create flasbased grid disck DG_FAST.
    2. Create the same Grid disk DG_FAST on storage server 2.

    Not sure...how this will work may be you can give a try
  • 5. Re: tablespace on flash cache
    BobCarlin Explorer
    Currently Being Moderated
    It would be interesting to know why you might want to create your object in flash cache

    Regards
    Bob
  • 6. Re: tablespace on flash cache
    robinsc Explorer
    Currently Being Moderated
    With he latest storage server software and write back flash cache there is very little reason why one would want to put tables in flash based grid disks ( which is what I assume this questionis about) Rathe rit makes much better sense to use all your flash memory as flash cache and selectively set the CELL-FLASH-CACHE keep storage option for tables of interest.

    And strictly speaking flash cache is a storage extension since it speeds up IOPS and MBPS and is accessed via scsi calls.

    Edited by: robinsc on Dec 11, 2012 12:35 PM
  • 7. Re: tablespace on flash cache
    LaserSoft Journeyer
    Currently Being Moderated
    Hi Friend,

    You can configure a smaller Exadata Smart Flash Cache and use the remaining flash memory as a flash disk drive. You can then create grid disks based on flash memory.

    These flash disks can be used to configure high performance ASM disk groups housing their own tablespaces.

    In this case, the flash memory is not used to cache data, rather it becomes a high performance permanent store for some of your data.

    Hope it Helps...

    Thanks
    LaserSoft

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