Re: Curiosity question - Bandwidth using RMAN duplicate from Serivce

On 3/1/19 2:46 AM, Oleksandr Denysenko wrote:
> it looks like I have missed something...
> 350GB/hr=350*1024=358 400MB/hr=358 400MB/(3600sec)=99.55MB/sec, not
> 7.5MB/sec which is too low...

Thank you for correcting me. You, of course, are right. My math was wrong.

> 99.55MB/sec definitely is about the limit of 1Gb/s Ethernet.

Yes, but not even with 10Gb/s Ethernet will you get much larger number. I have no explanation. I needed 4 channels on each DB node of half rack Exadata X6, with Oracle 12.1 to fully saturate 10Gb/sec Ethernet.

> if compression is used to save network bandwidth than core performance
> may be the bottleneck for the channel, so more channels required.

That may be the case. I am not quite sure about the cause. With NetBackup 6.5, the last version I've used as a DBA, I've got similar albeit a bit lower numbers. Version 6.5 did not have deduplication turned on and I've used "BACKUP AS COMPRESSED BACKUPSET".  With Commvault, I advise against that because Commvault deduplication works best with LZOP compression algorithm, which is Commvault's internal compression algorithm. RMAN compression, on the other hand, is either gzip or bzip2.  Of course, to use bzip2, the client must have advanced compression license. Neither gzip nor bzip2 work well with deduplication.

> I suggest to do several test and find real bottleneck:
> - if network bandwidth is not limited then don't use compression
> - if compression is used, than you may be limited with cpu at the
> original system
> - if nor network bandwidth nor original system cpu are limited, then
> look for original or target storage system bandwidth limitations
>
> Best Regards,
>
>   Oleksandr Denysenko
I am not quite sure that the customers would like me to test on their equipment. However, I am currently working with a customer running Oracle 18c on Exadata X7-2, where the database nodes are virtual and the backup destination is connected to the Exadata using Infiniband. I will post the result, if allowed to do that.

-- 
Mladen Gogala
Database Consultant
Tel: (347) 321-1217


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