Re: [9fans] fossil pb: FOUND!

[erik quanstrom <quanstro@quanstro.net>]

On Sat Jan 14 16:40:46 EST 2012, aram.h@mgk.ro wrote:
> > do you have any reference to ZFS being content-addressed storage?
> 
> It's not purely content-addressed storage, but it implements
> deduplication in the same way venti does:
> http://blogs.oracle.com/bonwick/entry/zfs_dedup (the blog post offers
> only a high level overview, you have to dig into the code to see the
> implementation).

content addressed means given the content, you can generate the address.
this is NOT true of zfs at all.

> > your claim was, random access is free on ssds.  and i don't see how these
> > numbers bolster your claim at all.
> 
> Maybe my wording wasn't the best, so I'll try again.  SSDs can do
> 100times more iops than HDDs for a given performance hit ratio.  In my
> experience, ignoring fragmentation completely leads to average
> fragmentation being significantly less than 100 times worse compared
> to a traditional filesystem that tries hard to avoid it. In practice,
> I've found that a fragmented filesystem on a SSD performs at worst 10%
> behind the non-fragmented best case scenario. I'd trade 10%
> performance for significantly simpler code anytime.
> 
> The phrase above is ignoring caching.  I've ran ZFS for many years
> without a SSD and I haven't noticed the fragmentation because of very
> aggressive caching (see the ARC algorithm).

you keep changing the subject.  your original claim was that random
access is not slower than sequential access for ssds.  you haven't backed
this argument up.  the relative performance of ssds vs hard drives
and caching are completely irrelevant.

- erik