How to create a datastore with small blocksize

[robertortel]

Hello,

I want to create a datastore out of two 160 GB disks. All the VI Client allows me to do is to create a whole disk datastore with 1 MB blocksize. But for performance reasons with the virtualized Oracle RAC which is 8K organized, I want to come down to a smaller blocksize. But how?

Is there any way of splitting my disk into (lets say) four parts, each having a smaller block size and putting them all together as extends into a datastore? To create partitions with fdisk does not work, as the VI Client wants to use the disk unpartitioned. Any ideas?

Robert

[LarsLiljeroth · Accepted solution]

Hi

That's not possible. The smallest blocksize is 1 MB on a VMFS partition.




Best regards

Lars Liljeroth

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[robertortel]

I wonder, if there really is a performance issue. The current storage is not very fast, so that unnecessary IO would hurt a lot. If I do a 8K write to a 1 MB disk block, is then the whole block rewritten (1 MB) or only the net size (8K)?

Reads are not important, because the whole database is in-memory (after warm up).

Robert

[riker82]

which file system are you using on that vm?

[robertortel]

The data is managed as

RawDevices --> Oracle ASM --> Oracle Database

Robert

[riker82]

If you prefer to have best Oracle practise, It's better if you use also RAW Vmware disk device instead of vmdk.

What do you think?

[robertortel]

Ok, but how to do this? Do I have to create partitions (fdisk?) to map them into a VM? How to map them? But then I loose the Striping-RAID-like feature of my datastore, which is using two disks.

Robert

[riker82]

how to do this? <--- it depends. What kind of storage are you using? DAS? NAS? or SAN?

Do I have to create partitions (fdisk?) to map them into a VM? <-- you have only to assign the luns to your esx farm (LUN MASKING), after that, you have to assign each lun to vm you need.

How to map them? But then I loose the Striping-RAID-like feature of my datastore, which is using two disks. <-- you can also use striping raid cause you can associate more than one RAW Lun to the virtual machine, and It can be threat as a vmdk with the Virtual Raw mode.

see Basic Administration guide at page 153 for vm config

see also Fiber Channel San configuration guide for best config.

[robertortel]

Thank you for your help, but there is something comming into my mind why raw mapping from DAS (this is what I have) into VMs is not an option: With this option enabled I would loose the capability to move the whole RAC setup to other VMWare products and hosts. The whole setup is for functional testing so performance is not the most important issue here.

I am interested in performance tuning here but to carry/transfer the Oracle RAC around is more important!

Robert

[riker82]

If you have a "not partitionable" or "not partitioned" DAS you cannot do anything.

the best way is having a SAN (in that way, you will have the possibility to move your RAC wherever you want)...

you cannot do so much with a das storage.

sorry.

Riccardo Barone