|
Re: [BackupPC-users] Block-level rsync-like hashing dd?
2011-04-12 23:17:59
Saturn2888 <backuppc-forum AT backupcentral DOT com> wrote
on 04/12/2011 10:40:50 PM:
> My goodness that's a lot of replies; although, almost all of them
> are from a post I made a while back which I've elaborated on at
> least 3 times since.
But you keep saying the same thing. Repeating it doesn't make it
doable.
> The main point here that I'm trying to get across,
at least for my
> own setup, is that I cannot handle dd'ing 1TB/day.
I'm very sorry to hear that. But you have *very*
little choice. Wishing it weren't so doesn't change it.
> That would
> literally take 8-12 hours (at least half a day) easy depending on
> network load, and it would cream available bandwidth.
By my math, that means you're moving about 24MB/s
(1TB/60/60/12 hours), so it sure sounds correct to me.
(As for 'creaming available bandwidth': you
can't add an additional PCI or PCIe Gigabit NIC to dedicate to the backup?
Or even better, put that extra NIC into a dedicated gigabit switch--even
a cheap one--so now your backup traffic never even appears on your normal
LAN? Not every problem can be fixed in software. But I digress...)
> The reason I
> am advocating DRBD is because I have it going to an iSCSI target on
> a machine with ZFS which snapshots the pool. The key there is I'm
> taking snapshots of it so even if it corrupts, I'm fine.
You think/hope/pray. Do you truly understand
ZFS snapshots? I guarantee that you *DO* *NOT*. Corrupt the
base layer, and all of the snapshots on top of it are *TOAST*.
But continuing anyway...
> All I'd
> have to do is mount the .img as EXT4 in an iSCSI target and point
a
> client to that target to retrieve the files.
This is in *NO* way different from pairing LVM with
iSCSI. Where does DRDB come into this?
> Not necessarily the
> best idea, but I don't see pool corruption a big deal because I've
> never experienced anything like that.
OK, then. If that's your philosophy (I've never
seen it so I won't worry about it!) then please feel free to use whatever
solution you would like. After all, if it's never happened to you,
then there's no need to protect against it!
> The BackupPC_copyPcPool script and the tar copy
are great for
> backing up the pool but both suffer the same fate as dd; there's no
> method of only transferring changes of files which destroys
> available bandwidth and leaves drives running constantly almost all
> day long slowing down crucial backups of machines.
Again, just because you keep loudly asking for something
doesn't make it possible.
That whole "figure out what has changed"
is not magically instantaneous. It takes a *lot* of work to actually
do that part. You keep ignoring that. Once you truly understand
and factor that work in, I think you will find that the dd solution is
not nearly as lacking as you think it is.
> And please note, I did talk about ddsnap as well.
While the
> project's out of commission, the software still exists somewhere.
And I covered that as well. It will read *exactly*
as many bytes as a dd will--and read a *lot* more bytes on the destination
side than dd will. Do not continue until you truly understand that.
The *only* thing it won't do is transfer as many bytes
over the wire. Is that *TRULY* what you are worried about?!? Again,
buy a $30 NIC and you will no longer worry about that any more!
And please do yourself a *very* big favor: make
*sure* you *truly* understand exactly what protection snapshots offer for
your data. (Hint: they make your data *less* reliable, not
more reliable.) I'd hate to see you put the safety of your data into
something that is not providing you with what you think it is.
Timothy J. Massey
------------------------------------------------------------------------------
Forrester Wave Report - Recovery time is now measured in hours and minutes
not days. Key insights are discussed in the 2010 Forrester Wave Report as
part of an in-depth evaluation of disaster recovery service providers.
Forrester found the best-in-class provider in terms of services and vision.
Read this report now! http://p.sf.net/sfu/ibm-webcastpromo _______________________________________________
BackupPC-users mailing list
BackupPC-users AT lists.sourceforge DOT net
List: https://lists.sourceforge.net/lists/listinfo/backuppc-users
Wiki: http://backuppc.wiki.sourceforge.net
Project: http://backuppc.sourceforge.net/
|
|
|
