v4 questions, crc's

v4 questions, crc's

[Tom Vier]

(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).

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())?

-- 
Tom Vier <tmv@comcast.net>
DSA Key ID 0x15741ECE

Re: v4 questions, crc's

[Hans Reiser]

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())?
>
>  
>

Re: v4 questions, crc's

[David Dabbs]

Tom, 

would you mind forwarding links to the IBM/Sun info you mentioned?

Thanks, 
 
David

Re: v4 questions, crc's

[Tom Vier]

On Thu, Jul 22, 2004 at 05:30:38PM -0500, David Dabbs wrote:
> would you mind forwarding links to the IBM/Sun info you mentioned?

i'll see if i can find it. i think the sun stuff was on slashdot. as far as
ibm, that was just from their tv commercials. they mention "self healing"
file systems.

-- 
Tom Vier <tmv@comcast.net>
DSA Key ID 0x15741ECE

Re: v4 questions, crc's

[Nikita Danilov]

Tom Vier writes:
 > On Thu, Jul 22, 2004 at 05:30:38PM -0500, David Dabbs wrote:
 > > would you mind forwarding links to the IBM/Sun info you mentioned?
 > 
 > i'll see if i can find it. i think the sun stuff was on slashdot. as far as
 > ibm, that was just from their tv commercials. they mention "self healing"
 > file systems.

No serious technical information of Sun ZFS is publicly
available. There is a couple of introductional papers by Valerie
Hensen (http://www.nmt.edu/~val/): http://ohm.hpl.hp.com/self-manage03/Finals/henson-self-tune.pdf

Nikita.

 > 
 > -- 
 > Tom Vier <tmv@comcast.net>
 > DSA Key ID 0x15741ECE
 > 

Re: v4 questions, crc's

[Tom Vier]

> > would you mind forwarding links to the IBM/Sun info you mentioned?

found it.

http://tinyurl.com/3a3yq

-- 
Tom Vier <tmv@comcast.net>
DSA Key ID 0x15741ECE