Re: Debian+LVM+RAID

On Sat, Jul 11, 2009 at 04:40:02PM -0600, lee wrote:
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.

just about the same thing



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.

Umm 1TB @ $115 = ~$2K

motherboard with 6 sata ~$200 + 2 x Adaptec SATA controllers ~$120 each


The drives were expensive yeap, but I have that much stuff (well once
you take out the backup server so 10 drivees and then raid6 - another 2
drives = ~8Tb worth of data which really equates to about 6T of data to
leave some head room)

so roughly ~$3K (aus dollars)



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
problems.

yes


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 ...

it all about making assumption we do it all the time, based on our
previous experiences.


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.

You don't run any https site nor use ldaps or ssl postgress connections.
I think you will find you system ssh keys are 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.

I would say that you are very lucky to not have to backup your /etc


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.

with raid you can mount the single partition and use it as is if you want,
but I would suggest to only do that in emergancies


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.

I have had faulty hardware - I got it fixed


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.

if you did it on such a regular basis why not write a script ?


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.

true


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.

raid is not a backup solution. there is always a chance !!something!!
might go wrong, I have tried to reduce that by having my !!complex(i
diss agree that it is)!! solution with a backup server to reduce the
chance of me loosing my vital stuff, for my really important data I also
copy to a server off site.


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 ;)

for now I still don't see any benefit, but at least I know about that
option for now





--
BOFH excuse #405:

Sysadmins unavailable because they are in a meeting talking about why they are unavailable so much.

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