[CentOS] Re: Planning Mail Server (with low resources)

[Bryan J. Smith]

Aleksandar Milivojevic <alex at milivojevic.org> wrote:
> Not true.  You can do backup on disk exactly the same way
> you do them to tape. With tape, you calculate how big your
> backups are, and for how long you want to keep them.  Then
> you go out and by that many tapes.  With disk, you do the
> same thing and buy disk(s) of appropriate size.  If you run
> out of tapes, you buy more tapes.  If you run out of disk
> space for backup, you buy more disks.  Same thing.

No, not the same thing.

Tape is removable and has higher G tolerances than 3.5" fixed
disks.  It is more portable _and_, unlike commodity disk, it
doesn't need to be spindled regularly.  3.5" fixed disk is
_not_ viable for storage.

That's why Removable Rigid Disk (RRD) was introduced.  It
increases shock tolerance, solves the other portability
issues, and is designed sit on the shelf.  Unfortunately,
other than being cheaper than tape in initial cost, it's more
costly in media and slower.

That's why the combination of fix disk and tape is _ideal_. 
You use fixed disk -- recommended "enterprise" 1.0M hour MTBF
"near-line" tolerance tested commodity fixed disk -- in a
24x7 backup server.  You then take select back-ups from that
server and put them to tape -- anything you're going to
off-line or take off-site.

Putting everything to tape means you're at the mercy of
successful tape backup.  That has proven to be a major issue
for everyone.  Putting everything to disk means you're at the
mercy of that disk, and 3.5" commodity disk does _not_ handle
G or off-line storage (even just a couple of weeks sometimes)
nearly as well.

[ SIDE NOTE:  In the worst case, I'd use 2.5" disks that can
take higher G tolerances.  They even have 5.25" bays that
hold six (6) 2.5" hot-swap SATA drives now. ]

> Anyhow, cost of single SDLT tape is comparable to
> cost of disk drive of same capacity.

400GB LTO-3 tape is under $100 by the dozens.  The smartest
thing I can recommend to companies that have a few servers is
build a single backup server with TBs of storage, and then
put one (1) LTO-3 tape drive on it.

You sync backups to the disks on that backup server during
the nightly backup window.  Then you commit select backups to
tape whenever you need to off-line something, such as a
weekly off-site tape.  Use disk for the immediate backup and
restores.  Use tape for the off-site or when you want to
off-line something for retention later.

With a single server, just get extra disk to keep redundancy
on disks off-list.  Then use a DVD-R and a minimal tape drive
(maybe an entry-level VXA) to off-site select itmes.

> The user is not going to bother to backup.  He'll just
> blaim you for loosing his email (no matter who's
> responsibility it was on paper). 

There is something to be said about making users responsible,
at least in a campus environment of students.

> Anyhow, as I said previously, for $100,000 (which would be
> price of USB sticks) you can buy really fancy storage with
> really fancy backup solution. 

Agreed.  Consider something like a Copan Revolution series:
  http://www.copansys.com/products/index.htm  

It's a FalconStor VTL system, which almost everyone uses.  It
run on Red Hat Linux 7.3.  Even Microsoft has one.  ;->



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