[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
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.
--
umka
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