[Lustre-devel] storing SOM epoch in EA
Alex.Zhuravlev at Sun.COM
Tue Feb 19 04:09:32 PST 2008
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)
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
> 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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