[kwlug-disc] Backup and Recovery in the 21st Century

Khalid Baheyeldin kb at 2bits.com
Tue Jan 12 11:16:32 EST 2010


On Tue, Jan 12, 2010 at 9:47 AM, Chris Irwin <chris at chrisirwin.ca> wrote:

> On Tue, Jan 12, 2010 at 09:29, Khalid Baheyeldin <kb at 2bits.com> wrote:
>
>> On Mon, Jan 11, 2010 at 11:52 PM, Chris Irwin <chris at chrisirwin.ca>wrote:
>>
>>> On Fri, 2010-01-08 at 18:50 -0500, Khalid Baheyeldin wrote:
>>> > Dump is a very old utility, yet very useful.
>>>
>>> It seems dump is not available for ext4 at present anyway, so I'm stuck
>>> with something else. I'm still somewhat curious what the actual benefit
>>> is. I saw some vague references to speed improvements (meh, it runs at
>>> night) and a comparison done on BSD systems in 1991. Other than that,
>>> there doesn't seem to be much info on why it is a better choice, just
>>> that it works differently.
>>>
>>
>> The fact that it does incremental backup natively, understanding the
>> difference between a full and an incremental. It also does many levels
>> of incremental if you need that (Tower of Hanoi scheme).
>>
>> The fact that it works on the file system level also has advantages. You
>> can restore a partition EXACTLY to what it was before. This means
>> timestamps, ownerships, access times, ...etc.
>>
>
> That would be advantageous. I wonder if there will be ext4 support in the
> future. From a mail list entry from Theodore Ts'o, it looks like if you
> modify dump to remove the capability checks on the file system, it "should"
> work fine for ext4.... I'm not keen on being the first to test that...
>

Agree here. I hope dump catches up soon. Otherwise I will stay with ext3 if
it does not.


> How is a dump in terms of file size compared to tar? Does it still make
> sense to pass through gzip? (Understanding that benefit of gzip varies
> depending on data)
>

An incremental dump varies depending on how many files you change per day.
A full dump is about the same size as the file system you are backing up
(without
any compression).

In general I prefer not to compress backups. From the days I used tape, if
you
have a compressed backup and there is a glitch at some point in the media,
then
everything after it is not restorable. If you have no compression, then only
the file
that has the glitch is bad, but all files after it are restorable.

This is different today because I/we use disks, but still a matter of habit.

In my case, a server backup is around 250MB for incremental level 1 on
Monday,
and grows each day since I don't use other levels. By Saturday it is around
850MB.
Then a full backup is done on Sunday (around 80GB, the entire server).

I could reduce the size of daily backups if I use level 2 for Tuesday, 3 for
Wednesday,
....etc. This would have the advantage of less size, but the disadvantage of
complicating
restores. By taking just level 1 backups each day, I need the last full and
the last incremental for a full restore, rather than multiple incremental
restores.
-- 
Khalid M. Baheyeldin
2bits.com, Inc.
http://2bits.com
Drupal optimization, development, customization and consulting.
Simplicity is prerequisite for reliability. --  Edsger W.Dijkstra
Simplicity is the ultimate sophistication. --   Leonardo da Vinci
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