[CentOS] Re: Opteron Mobo Suggestions -- the follies of typical tape backup (it's the 21st century)

[Bryan J. Smith]

On Wed, 2005-06-22 at 13:36 -0700, Kirk Bocek wrote:
> Well, now you're giving me a reason to spend the money -- the 3Ware 
> ports have better performance than the nForce ports.

What I said in response to your comment on wanting NCQ support on an
individual is that an "intelligent" controller like a 3Ware "Storage
Switch" with an ASIC and SRAM is doing _exactly_ what NCQ does, only far
more intelligently (for _all_ disks in the array).

3Ware has repeatedly taken benchmark award after benchmark award in its
ability to queue I/O requests better than any other ATA RAID option out
there (and even most SCSI RAID ones too).  How?  Because it's not a
buffering disk controller with DRAM, it's a switching ASIC with 0 wait
state SRAM.

That means it's ideal for when you're just throwing data around.  Things
change though if you're doing more buffering (like RAID-5).  That's why
3Ware introduced the 9500 series (to add DRAM buffer to its existing
ASIC+SRAM design).

> I wasn't clear that this is for *off-site* backup.  I have plenty of 
> on-line backup going on. I need to be able to take the backup away so we 
> have something to fall back on when the building falls down, burns up or 
> otherwise goes away. Tape serves this function nicely. But a hard-drive 
> would be faster and more flexible.

I know this.  I never thought otherwise.  I wasn't even debating the
merits of tape v. disk (that was someone else).

What I was stating was that you _never_ want to use "consumer" buses for
server storage.  Despite Apple's insistence that FireWire is server-
grade, they've had lots of issues.  Yes, it's better than USB and far
more intelligent (e.g., USB can't do device-to-device, FireWire can).

I was saying further is that if you are using USB or FireWire so your
backup drive is "removable," you should consider _other_ options.

1.  External SCSI

SCSI just works and works well, and FireWire will get there someday on
servers (it's already much, much better for consumers, I agree wholly).
You can also safely unload/reload the SCSI modules in the kernel for the
device that controls the tape when you want to remove the tape (assuming
nothing else is on the SCSI card).

2.  Backup over NIC to a "near-line" device with the tape drive

I'm not talking about on-line backup to disk.  I'm talking about
centralizing your backup to a system that is both a "near-line" disk
_and_ can commit to tape for your other systems outside of their backup
windows.  Especially when your budget is limited and your tape devices
are X servers to 1-2 tape drives.

Most sysadmins think they have to do their tape backups in "full" in
"real-time" during their "backup window."  Even when they do centralized
backups, they do them in "real-time" and that means they are sending
_all_ data over the network.  This is wholly unnecessary and
inefficient.

  End-servers -> (rsync) -> "Near-line" storage server 
                         -> (attached) -> Tape Drive

Just pick a system to be the "near-line" storage server and put your
limited tape resources on it.  Now to 1 full rsync from each server to
it in their backup window.  You can spread this around a few days for
this "initial rsync" if it will take more than 1 evening.  Once you have
all systems "initial rsync'd" to the "near-line" system, all you ever
need is the incremental rsyncs to mirror the data.

Because once you have that data on the "near-line" device with the tape
drive, it's a matter of committing to tape locally whenever you feel
like it!  Anytime, anyhow, 24x7!  No more "rush" to get data to tape
during the backup window, that's what the near-line device does.  All
the servers have to do is push an rsync of changes during their window.

Whether you decide to do this on your "normal" network, build an "out-
of-band" (i.e., 2nd NIC in each server) network, or a more formal
"storage area network" (SAN -- be it FC-AL or GbE/iSCSI), that's up to
you.

> Are you saying that USB/1394 hot-plugging is unstable or unreliable?
> Do you possibly have any articles to point to?

I've have had to take baseball bats to people with Mac XServe as well as
PC servers running both Linux and Windows over the last 2 years because
they keep plugging in FireWire and USB devices and wonder why their
servers crash.  Not even Apple has perfected FireWire as a replacement
for SCSI on _servers_.

If you want to be able to have only 1-2 tape drives for far more servers
and workstations, I really recommend you build a dedicated system just
as a "near-line" backup server and put the tape drive on it.  Now you
just send rsyncs of systems to the "near-line" backup server and commit
to tape as you see fit from those local stores.

SIDE EFFECT:  If you need to restore something immediately, you don't
always have to go to tape!  If you are already doing this, then just put
your tape backup on those systems with the "on-line" storage.

Simple, no?


-- 
Bryan J. Smith                                     b.j.smith at ieee.org 
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