Re: Backup Software?
From: Daniel Rudy (nospam_at_die.spammer.die)
Date: 01/28/05
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Date: Thu, 27 Jan 2005 18:26:36 -0800
<abram@mailinator.com> wrote in message
news:1106862183.941199.176690@c13g2000cwb.googlegroups.com...
> Just a few notes due to the lack of time.
>
> From
> http://www.acronis.com/enterprise/products/ATIESWin/features-imaging.html
> :
>
> <<Acronis True Image 8.0 Enterprise Server for Windows allows you to
> create the exact server disk image for complete backup providing the
> comprehensive and cost effective server protection....
> Backup only the ****necessary**** server disk sector contents
>>>
>
> The key word is "necessary". Who desides what is necessary? If Acronis
> backs up only "necessary" content, then it's not true imaging, is it?
> If a "true image" contains only "necessary" data, then how is it
> different from a file system backup?
>
> Next, there's no such thing as "the exact server disk image" of a
> running system, in any practical sense. There may be exact images of
> offline disks, not of an active Windows system partition.
>
> Say I have an application that writes to file. I have some file data
> cached in my application, some data is cached by the file system, the
> rest of the data is physically on HDD. When any "true imaging"
> software
> tries to make a "true image", the best it can do is flush the file
> system buffers, and create an image of the file that doesn't contain
> the data cached by my application. Due to the structure of the file,
> that cached data is important, and the file is invalid without that
> data.
>
> What we've got is a corrupted image of the file, that won't work with
> my application if restored from the "true image". See "I have complex
> applications such as Microsoft SQL Server..."
> http://www.acronis.com/enterprise/products/ATISWin/faq.html#19.
>
> It is in theory impossible to handle the case above without
> interacting
> with my application. That's when the volume shadow copy service,
> supported by NTBackup, comes forward. The shadow copy service tells my
> application to flush all the buffers and suspend all writes, so that a
> coherent copy of the file can be taken. It's a bit more complicated
> that just sector-by-sector copying, isn't it? If Acronis doesn't
> support shadow copies, then it's not true imaging. If it does then
> it's
> not true imaging anyway since many applications doesn't support shadow
> copies either, and they must be stopped to make true images of their
> data.
>
> The summary. "True images" created by so-called "true imaging"
> software
> are no more, if not less, "truer" than NTBackup's backup sets.
>
You bring up a very interesting point. Granted, this is a little
off-topic, but in Unix systems, you have tar and cpio. Tar or Tape
Archive is a file oriented backup while cpio is a sector oriented
backup. Futher more, on my FreeBSD machine, I can do tar -czvf
filename.tar / and back the entire machine up to one file. But, the
necessary data is in /home, /usr and /var. You still have to reinstall
the operating system though.
I define a true image as a sector by sector copy. One way to get around
the problem with open files is to boot the machine from a second
installation of Windows on another HD and backup the system that way.
Unfortunately, this requires the machine to be rebooted and application
downtime while the backup is made. But, on the positive side, you have
a true image of the harddisk.
> ----------
>
> If someone states that XP's and later NTBackup is legacy, they show
> their ignorance. NTBackup is far from ideal, but it is maintaned by
> Microsoft who knows more than anyone about Windows file systems. In
> fact, BackupExec and BackupMyPC (they come from the same source as
> NTBackup) are more legacy than NTBackup since they don't support the
> new minitape driver model, and they don't work with tape drives
> unknown
> to them. As opposed to NTBackup, which works with any tape drive, as
> long as a correct minitape driver is provided by the manufacturer.
>
> NTBackup targets tape drives just because the tape is the most
> reliable
> high-capacity media. I would rather blame NTBackup if it supported
> CD/DVD and not tapes.
>
> --
> http://www.firestreamer.com - NTBackup to DVD and DV
>
> PS. Al, I don't blame you. I just wasn't sure which post to reply to.
>
>
>
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