[Lustre-devel] storing SOM epoch in EA

Yuriy Umanets Yury.Umanets at Sun.COM
Tue Feb 19 04:02:02 PST 2008

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 

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.



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