Re: [9fans] Q: moving directories? hard links?

[dexen deVries <dexen.devries@gmail.com>]

On Friday 22 of April 2011 10:03:52 Bakul Shah wrote:
> On Thu, 21 Apr 2011 18:41:25 EDT erik quanstrom <quanstro@labs.coraid.com>  
wrote:
> > > IIRC companies such as Panasas separate file names and other
> > > metadata from file storage. One way to get a single FS
> > > namespace that spans multiple disks or nodes for increasing
> > > data redundancy, file size beyond the largest disk size,
> > > throughput (and yes, complexity).
> > 
> > that certainly does seem like the hard way to do things.
> > why should the structure of the data depend on where it's
> > located?  certainly ken's fs doesn't change the format of
> > the worm if you concatinate several devices for the worm
> > or use just one.
> 
> ?
> 
> It all boils down to having to cope with individual units'
> limits and failures.
> 
> If a file needs to be larger than the capacity of the largest
> disk, you stripe data across multiple disks.  To handle disk
> failures you use mirroring or parity across multiple disks.
> To increase performance beyond what a single controller can
> do, you add multiple disk controllers.  When you want higher
> capacity and throughput than is possible on a single node, you
> use a set of nodes, and stripe data across them. To handle a
> single node failure you mirror data across multiple nodes. To
> support increased lookups & metadata operations, you separate
> metadata storage  & nodes from file storage & nodes as lookups
> + metadata have a different access pattern from file data
> access. To handle more concurrent access you add more net
> bandwidth and balance it across nodes.

<![RANT[
except those are not 100% orthogonal. not in theory, and even less in 
implementations. you risk ending up with big-ball-of-mud code, or abstracting 
all your performance (and flexibility and metadata like S.M.A.R.T.) away.

also, (almost every) network hop and node lessens the compound reliability; 
some even introduce entirely new failure modes.
]]>

so kudos to Isilon for actually having build great stuff :)


-- 
dexen deVries

[[[↓][→]]]

``In other news, STFU and hack.''
mahmud, in response to Erann Gat's ``How I lost my faith in Lisp''
http://news.ycombinator.com/item?id=2308816