I'll give you a 10 for good linguistics. [although, heck, I still don't agree, since there never is a copy of the data]

The way I see it: Regarding log-structured, you are describing additions to standard filesystems to log prior to write (generally for reboot consistency), such as Sun's UFS w/ Logging in Solaris 7. That is not a log-structured file system. Do a quick search on log-structured file systems, and you'll see many other implementations. For example (of a paper): (apologize for the long url) http://citeseer.nj.nec.com/cache/papers2/cs/698/http:zSzzSzwww.eecs.harvard. eduzSz~margozSzpaperszSzusenix.193.pdf/seltzer93implementation.pdf

Paul -----Original Message----- From: Traitel, Eyal [mailto:eyal@netapp.com] Sent: Sunday, May 13, 2001 10:43 PM To: Paul Timmins; 'Eli Lopez'; Jay Soffian; toasters@mathworks.com Subject: RE: Copy on write - Netapp vs. others

Paul,

I think this is only terminology issue. The word "copy" was probably used as a noun, not a verb, with the meaning that after the write, you have another copy of the same block - well, not exactly the same - one is the old, one is the new. Hence the word copy.

On log structured fs - if WAFL was simple and not patented everyone could have just do it like us. This is not the case. Regular log based filesystems have to commit once in a while the log into the original, fixed locations on disk. WAFL does not have this limitation - that's the Anywhere from the word WAFL.

Eyal.

---------------------------------------------------------------------- eTraitel - I'm the new eBuzzword around !!! ---------------------------------------------------------------------- Filer Escalation Engineer CNA, MCSE, CSA, LCA, NetApp CA

Network Appliance BV Hoofddorp, The Netherlands Office: +31 23 567 9685 Cellular: +31 6 5497 2568 ---------------------------------------------------------------------- Get answers NOW! - NetApp On the Web - http://now.netapp.com ----------------------------------------------------------------------

-----Original Message----- From: Paul Timmins [mailto:paul@ptimmins.com] Sent: Mon, May 14, 2001 04:06 To: 'Eli Lopez'; Jay Soffian; toasters@mathworks.com Subject: RE: Copy on write - Netapp vs. others

Not to nit-pick... but what being described is the behavior of a log-structured file system (of which WAFL is one). There are many other implementations of log-structured file systems.

IMO, calling that copy-on-write is dead-wrong, not merely confusing. There's no copy going on. The inode file is copied (checkpointed) when a snapshot is initiated, not when a write occurs.

Just my two cents... Paul

-----Original Message----- From: Eli Lopez [mailto:elopez@netapp.com] Sent: Sunday, May 13, 2001 4:38 AM To: Jay Soffian; toasters@mathworks.com Subject: Re: Copy on write - Netapp vs. others

Hi Jay,

You are right that the terminology is confusing.

One way to look at it is to think of two ways of copy-on-write: when you are updating a block of a file you can: 1) Either write the NEW UPDATED block to a new location 2) Or move the OLD block to a new location AND THEN write the new updated block in place of the old one.

Taking a snapshot with both methods involves copying the inode file BUT obviously there could be serious performance impact using the second method (for each update, the write request needs to 'wait' until the old block gets copied to a new location).

Network Appliance's WAFL uses the first method which does not have any impact on performance and is (IMVHO) much more elegant.

Thanks, Eli

______________________ Eli Lopez Systems Engineer Manager Network Appliance, Israel (+972) - 50 - 304 - 733 Eli.Lopez@Netapp.com ______________________

----- Original Message ----- From: Jay Soffian jay@loudcloud.com To: toasters@mathworks.com Sent: Thursday, May 10, 2001 7:00 PM Subject: Re: EMC IP4700 vs NetApp F740

"Ferd" == Ferd Berfl ferd_berfl@yahoo.com writes:

> re: snapshots, I thought that everyone else's snapshot
> functionality other than Netapp's must be based on a "copy on
> write" method because Netapp has a patent on continuously
> writing new blocks.

WAFL uses copy-on-write. Here, straight from the horse's mouth:

WAFL uses a copy-on-write technique to minimize the disk space that Snapshots consume.

http://www.netapp.com/tech_library/3002.html

Now, Netapp's implementation may be unique, but to say that WAFL doesn't use copy-on-write and to make a claim like "copy-on-write is slow, Netapp doesn't use it" is bogus.

j.

Jay Soffian jay@loudcloud.com System

Administrator

408 744 7584 Loudcloud,

Inc.