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Old 01-29-2016, 09:24 AM   #16
MensaWater
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Not knowing the source of what you quoted I can' be sure what the author meant by "standard". "Default" setup on both UNIX and Linux is to write to filesystems (a/k/a "cooked" devices) and those will generally be on top of block devices.

Databases sometimes will allow or require raw devices. When using raw they are controlling exactly how the space is utilized within the database software itself.

ASM is a raw device methodology used by Oracle RAC/GRID. ASMLib is a additional tool Oracle created to facilitate use of ASM devices. In RHEL5 ASMLib was available but with RHEL6 it wasn't unless you downloaded and compiled the source yourself. You could however (and we do here) use ASM by defining your own udev rules rather than adding ASMLib. I've not checked RHEL7 to see if they've added ASMLib back to it.

I haven't checked it in a while but I doubt RAC/GRID has changed to allow "cooked" filesystems for storage. At one point they did allow for a specialized filesystem, OCFS then OCFS2, that made use of Linux' DIRECT_IO ability. We ran OCFS on RHEL5 but on change to RHEL6 we saw indications Oracle was deprecating OCFS/OCFS2 in favor of ASM so we did ASM.

Oracle has their own fork of Linux derived from RHEL that they call OEL and I gather it includes ASMLib. Here we prefer not to give Oracle control of the OS in addition to the DB because we find them quite rapacious in their licensing and support.
 
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Old 01-29-2016, 10:23 AM   #17
Joy Stick
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Hello Mensa Water

I read one link from OTN (Oracle Technology Network)
Exactly Someone asked my exact confusion (4 yrs before)

Snippet from OTN link

PHP Code:
According to my knowledge ASM feature support two different types of IO
1. Standard UNIX IO.
2. ASMLib IO.
Please help me in understanding the diferences between these two IO and in what occucations we go for each type of IO
https://community.oracle.com/thread/2169370?tstart=0

I searching answer exactly author's own question from given link
I do not understand given answers by some experts because i am also RAW

Thanks in advance !
 
Old 01-29-2016, 03:32 PM   #18
MensaWater
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There's been various changes to things since 2011. RHEL4 is no longer around. RHEL5 is but is very long in the tooth.

Like one of the posters on the link mentioned I have difficulty believing there is an issue using ASM on multipath vs ASMlib. Also the post seems to imply the user was using block devices vs the raw devices udev allows for (and what we use on RHEL6 with ASM vs ASMLib). As I mentioned there was a filesystem you could use for RAC/GRID called OCFS but it was using DIRECT_IO which isn't exactly the same as a standard filesystem like ext2/3/4 would use.

Also it isn't clear from the post whether the use case was actually RAC/GRID. You can do (and we do here) very large databases on standard "cooked" filesystems so don't need ASM/ASMLib/Raw at all for non-RAC/GRID databases.

Another complication is that RAC/GRID by default tries to impose its own redundancy on devices presented to it which you don't need if you're using RAID devices in the first place and may not want to if you're doing multipath depending on what the underlying storage uses. Here we have SAN presented storage created from RAID on back end disk arrays and we present it via 2 or more paths so there is absolutely no need for (and some detriment to) Oracle GRID trying to impose its own redundancy on top of that.
 
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Old 01-29-2016, 08:22 PM   #19
Joy Stick
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Ok Mensa Water ,

Whether the database env is STANDALONE/RAC/GRID (does not matter).

My only need is difference between Standard UNIX IO Vs ASMLib IO (for standalone or rac databases) ?

Does I/O happens different for both options ? (Above bold marked)
 
  


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