[Lustre-devel] storing SOM epoch in EA

[Alex Zhuravlev]

I guess there is some sort of misunderstanding here.

we don't need fid->epoch mapping. we only need epoch along with other
inode attributes. epoch is fixed size (8 bytes, probably few more for
flags in future)


thanks, Alex


Yuriy Umanets wrote:
> Alex Zhuravlev wrote:
>> Yuriy Umanets wrote:
>>   
>>> EA is separate block is evil. It makes things slow.
>>>     
>> we have fast EAs (stored in inode, this is why we make them large) for years.
>>   
> Well, people used horses for ages but this did not stop them from 
> building cars :) Guys, I gave you idea, not worse than using EAs. I will 
> not insist it is great. If you can't estimate its value yourself, well, 
> let it be. We have such a nice thing as IAM and you keep talking about 
> EAs...
> 
> Seriously, IMHO what is bad about EAs:
> 
> 1. You need to control their size, you need to bother;
> 2. Large-fast inodes make create/lookup slow. You need to load this 
> thing to memory after all. I think this is complement to additional 
> seeks caused by IAM;
> 3. Storing epoch in EA makes you use this chain to access epoch: 
> fid->inode->epoch (in EA), IAM makes it shorter: fid->epoch (in IAM);
> 4. Large inodes consume more RAM;
> 5. There others...  but they are less related to technical 
> downsides/advantages so I will omit them.
> 
> Thanks.
>