Re: v4 questions, crc's

[Hans Reiser <reiser@namesys.com>]

Tom Vier wrote:

>(resending)
>
>are wandering logs like rcu? unless i'm reading it wrong, it sounds like you 
>create a copy of the node, but with the updated pointer. you go up the tree, 
>creating updated parents, and the whole new path is finally committed when 
>the highest node's pointer is updated, right? how big are nodes in v4? 512 
>bytes? when updating a tree path, it causes a lot of single sector writes to 
>different areas (far apart?) but the only dependence is that all the new 
>updated versions of the nodes must be written before the top node is, right? 
>does v4 use extents? if not, how are the data blocks finally pointed to?
>
>sun has (or is writing) a new fs i read about recently that has data crc's 
>with error correction (i guess that's what the new "self healing" buzzword 
>means - i've heard ibm using it in commercials). i've thought about writing a 
>v4 plugin. i'm not sure how fine grained to make it. one crc for the whole 
>file isn't feasable. are blocks variably sized in reiserfs? perhaps each 
>extent or whatever could be crc'ed, with the crc's stored as metadata (using 
>whatever method v4 provides for saving variable length metadata).
>  
>
Putting a crc in every node would be easy to code and useful to users.

>also, what should i do if a crc is bad? just write to syslog? refuse to 
>return the data since it might be bad (return an error from read())?
>
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