[SLL] Rant: ATA-over-Ethernet 0x88a2

[Jesse Keating]

On Thu, 2005-05-05 at 14:04 -0700, Andrew Sweger wrote:
> But keep in mind this is going in another direction (from where I'm
> looking at the problem). I don't want a device that requires
> configuration
> through an embedded OS web interface (or whatever). Not to mention the
> lack of filesystem abstractions across discrete storage units (e.g.,
> md,
> lvm, etc.). As soon as it has power and gets a link from the switch,
> it's
> live. There's no TCP or IP stack involved. No applications. Just
> devices
> and ATA "packets". I've already got computers and they're loaded with
> applications for talking to data. I can't shoehorn any more drives
> into
> the chassis and I can't afford to keep replacing the disks with bigger
> ones every year or two (and throwing out the old drives just because
> they're half as big as the ones I'm using now). My plan is to have at
> least 3TB of storage on-line at home in the next year and have it as
> cheaply as possible (including not buying new hard drives). Why is
> another
> story altogether (I don't have to insert music CDs anymore and I'm
> about
> to do the same to DVDs). In two years, I want to be pushing 8TB. Three
> years: 40TB.

I've been down this road before.  Unless the AoE has enclosure services,
this will fail horribly.  

First) ATA is a horrible code set to start with.  I really hope that it
is ATA in name only, and that it borrowed most it's code from the SCSI
stack.

Second) Without some high level enclosure services, any type of array
you make out of these disks on the network will be extremely fragile.
If one disk goes down, your array will stop responding at all until you
completely power off and power back on minus the dead disk.  Or if you
even have network congestion or a network failure, it will bring the
whole thing crumbling down.

Third) Network overhead.  When you've got one or two of these disks
attached to even a gigabit network you're OK.  When you've got 3TB worth
of 40~80 gig drives sitting on your network, your network overhead is
going to be huge.  Thats just a ton of data to try and break up and send
out to all those disks.  Even w/out the TCP/IP overhead, you've GOT to
have some sort of delivery assurance mechanism to ensure your data gets
where it is going.  Thats going to require a bit of cross talk for each
write/read operation.  If you're doing some sort of RAID level ( I can't
imagine NOT ) then you're going to have metadata being shifted around a
bunch as well.

So now you're looking at maybe a dedicated gigabit network JUST for the
storage, and even that won't scale all that well with a LOT of small
devices.  Just too many devices to talk to.

My opinion is that this technology is good for a single disk or two for
family network storage.  Any type of array stuff is just beyond the
scope of the technology and asking for trouble.  iSCSI is even having
problems with this, and with multiple concurrent accesses and stuff.
Fibre Channel seems to have it nailed down, but MAN what a price you
pay.

-- 
Jesse Keating RHCE      (geek.j2solutions.net)
Fedora Legacy Team      (www.fedoralegacy.org)
GPG Public Key          (geek.j2solutions.net/jkeating.j2solutions.pub)
 
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