Re: anyone tried NVME in ODA?

  • From: Mladen Gogala <gogala.mladen@xxxxxxxxx>
  • To: oracle-l@xxxxxxxxxxxxx
  • Date: Mon, 30 Jan 2017 21:04:39 -0500

On 01/30/2017 11:24 AM, Ls Cheng wrote:

Expected to reach same IOPS as ASM on future 12.1.2.10.0 with fix 24930950.

I don't think it's a reasonable expectation. ACFS is a fairly complex layer on top of ASM. It is a cluster file system, which means that it must synchronize FS cache on all nodes that have mounted the file system. It also has to manage free space, probably using bitmaps. To add an additional layer, ACFS is an extent based file system, so it also must manage extent maps and windows. Also, ACFS is implemented as a userfs, which means that open,close, read and write system services have another level of indirection to go through, which is not the case with drivers that are implemented in the kernel.
Long story short, ASM is as close that you can get to raw disk and still have it manageable. There is a lot that needs to happen on top of ASM, to present it as a file system. The same is true for raw devices: there is a lot that needs to happen on top of raw disk, to present it as an Ext4 or NTFS file system. This is essentially the old debate: is the raw disk better than the file system, which was all the rage on this list in the times of oracle 7 and 8. ASM is more complex to manage but provides better performance. And it always will. I don't expect ACFS to match the raw ASM performance any time soon. The reason is simple: ACFS is another complex software layer on top of ASM.
The important question is whether the raw IO performance is more important than manageability. If your answer is "yes", you will probably want to use ASM. If your answer is no, you will probably want to use ACFS. Let's not forget that ACFS has a lot of very desirable goodies like snapshots, ACL and tagging. There are very good reasons for using ACFS. It all depends on your priorities.


--
Mladen Gogala
Oracle DBA
Tel: (347) 321-1217

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