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Re: Debian+LVM+RAID

On Fri, Jul 10, 2009 at 07:04:26AM +1000, Alex Samad wrote:

> comes down to how much you value your data.

It comes down to how much money you can spend on securing it.

> My home server has 10 x 1T drives in it a mix of raid1 + raid5 +
> raid6, I have a second server with 9 x 1T drives in it (in the
> garage) to do my backups - because it would take too long to send
> off site and I don't want to spend money on a tape system - i value
> my data - well I could afford to throw money at the problem.  But I
> have some important info there, photos & video of my daughter etc
> ...

Well, that's like $3000+ you spent on the drives alone, plus about
another $2000 or so for the controller cards. About $8k in total? Then
replace at least the disks about every three years. I don't have that
kind of money (and not that much data). And the more drives you have,
the more disks can fail.

> > I'm not afraid of that. But the point remains that having less md
> > devices reduces the chances that something goes wrong with their
> > discovery. The point remains that reducing the complexity of a setup
> > makes it easier to handle it (unless you reduced the complexity too
> > much).
> Ok to take this analogy even further why have 1T drives, why not stick
> with 1G hard drives - less data less chance of errors.

Yes --- but you probably have a given amount of data to store. In any
case, the more complexity your solution to store the data involves,
the better the chances are that something goes wrong. That can be
hardware or software as well as the user making a mistake. The more
complex a system is a user is dealing with, the easier it is to make a
mistake --- and software or hardware you are not using can't give you

> If you are building a large system or !!complex!! system, bit of
> planning before hand, I set mine up and haven't had a problem with md, I
> have lost some drives during the life of this server - the hardest thing
> is matching drive letter to physical drive - I didn't attach them in
> incremental order to the mother board (silly me)

Yeah, I know what you mean. The cables should all be labeled and
things like that ...

> > There's nothing on /etc that isn't replaceable. It's nice not to lose
> > it, but it doesn't really matter. If I lost my data of the last 15
> > years, I would have a few problems --- not unsolvable ones, I guess,
> > but it would be utterly inconvenient. Besides that, a lot of that data
> > is irreplaceable. That's what I call I a loss. Considering that, who
> > cares about /etc?
> really what about all your certificates in /etc/ssl, or your machines
> ssh keys,

There are certificates and ssh keys? I didn't put any there.

> or all that configuration information for your system mail,
> ldap, userids, passwords, apache setup, postgress setup.

It's easy to keep a copy of the configuration file of the mail server
on the /home partition --- and it's easy to re-create. There are only
two userids, no ldap, no postgres, and the config for apache is
totally messed up on Debian anyway since they split up the config file
so that nobody can get an idea how it's configured.

Anyway, you can always have backups of /etc; it's not changing very
frequently like /home.

> Admittedly you could re create these from memory but, there are some
> things that you can't 

If you have data like that on /etc, you need a backup.

> > What I was wondering about is what the advantage is of partitioning
> > the disks and creating RAIDs from the partitions vs. creating a RAID
> > from whole disks and partitioning the RAID?
> I have to admit I have evaluated partitioning + raid v's raid +
> partitioning, I think I would go with the previous, more system (old
> linux box, windows boxes, mac boxes ) understand partitions - where as
> not all OS understand raid + partitioning. And currently I don't see the
> advantage to raid + partitioning 

Hm, is it possible to read/use a partition/file system that is part of
a software-RAID without the RAID-software? In that case, I could see
how it can be an advantage to use partitions+RAID rather than
RAID+partitions. But even then, can the "other systems" you're listing
handle ext4fs? I still don't see the advantage of partitioning+RAID.

> I believe the complexity is not that high and the returns are worth it,
> I haven't lost any information that I have had protected in a long time.

Maybe that's because we made different experiences ... To give an
example: I've had disks disconnecting every now and then that were
part of a RAID. The two disks were partitioned, RAID-1s created from
the partitions. Every time a disk would lose contact, I had to
manually re-add all the partitions after I turned the computer off and
back on and the disk came back.

Since there were three partitions and three md devices involved, I
could have made a mistake each time I re-added the partitions to the
RAID by specifying the wrong partition or md device.

Now having only one md device instead of three doesn't offer that kind
of chance to get it wrong. If one disk would be missing, there's only
one disk I could add, and I don't have to worry at all about assigning
the right partitions to the right md devices.

To me, that is already an advatage of RAID+partitions. It may be a
small improvement, but things like that can add up. It's just so much
easier to maintain X simple things than it is to maintain X complex
things which provide the same functionality. The day might come where
two or three complex things go wrong at the same time and overwhelm
you with their complexity while you could have fixed them easily if
you had used simpler solutions.

> true, which is why I throw the book away and try different things some
> times, always good to learn new stuff

Hehe, try RAID+partitions ;)

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