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Does DAR have a target disc size limit?

Offline abarron

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Does DAR have a target disc size limit?
« on: May 31, 2015, 06:36:23 PM »
Hi,

My v9 server backups nightly to a locally connected USB drive of 3TB capacity. 

Fdisk -l reports the size as 3TB.

Disk /dev/sdb: 3000.6 GB, 3000592977920 bytes
255 heads, 63 sectors/track, 45600 cylinders
Units = cylinders of 16065 * 4096 = 65802240 bytes
Sector size (logical/physical): 4096 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0xee42fb5f

DAR reports:

Destination disk usage 330G, 48% full, 368G available
Backup successfully terminated at Sun May 31 02:12:41 2015

This suggests to me that DAR is only seeing around 700GB of a 3TB disc.

I have searched but can find no mention of a destination size limit (doesn't mean there is no such post of course)  anyone have any answers?

TIA.

Offline mmccarn

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Re: Does DAR have a target disc size limit?
« Reply #1 on: June 01, 2015, 12:00:28 AM »
[guess]
The first option that comes to mind is that the disk use and/or free space calculations in DAR are assuming 512 bytes per sector, so you get a number that is 1/8 of the actual.

I found this post from pcworld talking about 3TB drives:
http://www.pcworld.com/article/235088/everything-you-need-to-know-about-3tb-hard-drives.html

That article implies that there might be problems addressing drives over 2.2TB.  Perhaps the DAR calculations are overflowing and giving you results based on the remainder between 2.2TB & 3TB
[/guess]

Offline abarron

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Re: Does DAR have a target disc size limit?
« Reply #2 on: June 01, 2015, 09:57:56 AM »
Thank you mmccarn,  if this is the case is there anything I can do about it?

As you can tell I am inexperienced with Linux.

Offline mmccarn

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Re: Does DAR have a target disc size limit?
« Reply #3 on: June 01, 2015, 01:28:44 PM »
Here are the options as I see them:


1) Determine if the mis-reported stats from DAR affect actual performance, or are they just that - mis-reported stats. That is, does DAR fail when the reported available space reaches zero, or does it continue to work?

2) Replace the 3TB drive with something under 2.2TB

3) Research issues & solutions (open bugs and support questions) with Centos & the dar support mailing list.

4) Open a bug using the 'bug tracker' link at the top of this forum and hope that one of the developers knows more than I do about 3TB drives & DAR...


Offline abarron

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Re: Does DAR have a target disc size limit?
« Reply #4 on: June 01, 2015, 03:32:03 PM »
Thank you very much mmccarn, I will wait until the 'limit' is reached and see what happens and then follow your advice.

Offline Stefano

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Re: Does DAR have a target disc size limit?
« Reply #5 on: June 01, 2015, 03:34:02 PM »
Thank you very much mmccarn, I will wait until the 'limit' is reached and see what happens and then follow your advice.

IIUC you'll wait your backup to fail.. nice :wink: