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4 Replies Latest reply: Sep 20, 2011 7:26 PM by Hemant K Chitale RSS

Can DB files spawn disks in the same mount point ?

711242 Newbie
Currently Being Moderated
Hello Expert,

Can the Oracle Database files of 10.2.0.4 spawn across an disk in general and SOalris SPARC in particular.

What I mean by spawning is ?

I have an mount point /mnt1 which is made up of disk of 4 * 8GB disks. Toatal Size = 32 GB
Can I have an data-file in this mounbt point /mnt1 which is larger than 8 GB ?

I remember readind somewhere that estents can't spawn segments but segments can spawn data-files but data-files cannot spawn across disks.
Please help me confirm my concept.

Thanks in advance.

Regards,
Valli
  • 1. Re: Can DB files spawn disks in the same mount point ?
    sb92075 Guru
    Currently Being Moderated
    user4566776 wrote:
    Hello Expert,

    Can the Oracle Database files of 10.2.0.4 spawn across an disk in general and SOalris SPARC in particular.

    What I mean by spawning is ?

    I have an mount point /mnt1 which is made up of disk of 4 * 8GB disks. Toatal Size = 32 GB
    Can I have an data-file in this mounbt point /mnt1 which is larger than 8 GB ?
    YES
  • 2. Re: Can DB files spawn disks in the same mount point ?
    eric_grancher Newbie
    Currently Being Moderated
    Valli,

    if the mount point /mnt1 is a mounted filesystem which has the capacity of 32GB, then yes there is no problem for the Oracle database to have datafiles bigger than 8GB (actually as far as I know, the instance does not "know" that it is made of several disks, it just sees the filesystem).

    hope this helps,
    Eric

    PS: if you have four 8GB disks and the total size is 32GB, it means that no additional protection (RAID1, 10, 5, 6, etc.) is put at the OS level. So I assume that these "disks" are actually already protected by an underlying mechanism (like they are LUNs presented to the OS by a SAN who does the RAID 1,10,5,6,etc.). Otherwise with physical disks, your data would be in danger :-)
  • 3. Re: Can DB files spawn disks in the same mount point ?
    EdStevens Guru
    Currently Being Moderated
    user4566776 wrote:
    Hello Expert,

    Can the Oracle Database files of 10.2.0.4 spawn across an disk in general and SOalris SPARC in particular.

    What I mean by spawning is ?

    I have an mount point /mnt1 which is made up of disk of 4 * 8GB disks. Toatal Size = 32 GB
    Can I have an data-file in this mounbt point /mnt1 which is larger than 8 GB ?

    I remember readind somewhere that estents can't spawn segments but segments can spawn data-files but data-files cannot spawn across disks.
    Please help me confirm my concept.

    Thanks in advance.

    Regards,
    Valli
    "Spawn"? http://www.merriam-webster.com/dictionary/spawn

    How about "span" (the verb form) http://www.merriam-webster.com/dictionary/span

    As to your question . . . does Oracle see those separate disks? Or are they hidden behind some layers of abstraction at the OS?
  • 4. Re: Can DB files spawn disks in the same mount point ?
    Hemant K Chitale Oracle ACE
    Currently Being Moderated
    I remember readind somewhere that estents can't spawn segments but segments can spawn data-files but data-files cannot spawn across disks.
    The word is "span", not "spawn".

    A Segment consists of one or more extents. An extent is a contiguous group of datablocks. An extent, being part of a segment, can only belong to a single segment.
    Since a tablespace consists of one or more datafiles, it can have datafiles on different disks, different filesystems. The Segment is allocated extents amongst the datafiles (so it follows that a Segment can span datafiles).


    In the old days when Raw Devices were used, a datafile that was created on a raw device would only be within the raw device. If the raw device was carved out of a LUN on a physical disk, it would be contained within that physical disk. (However, it was still possible, on some platforms/storages to have a LUN carved out of multiple disks, thus spanning more than one disk).

    Unless a filesystem is created on a single disk (e.g. the boot or root disk of the server), filesystems generally are created to span disks. Thus, a datafile may span disks -- the datafile, itself, is not "aware" of which disks it is residing on.
    In ASM, a diskgroup generally consists of multiple disks. So a datafile in an ASM disk group may span disks.



    Hemant K Chitale

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