2016 ReFS and file allocation size

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Re: 2016 ReFS and file allocation size

Veeam Logoby chrmol » Thu Nov 17, 2016 7:25 am

Thanks Mike.
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Server 2016 ReFS

Veeam Logoby ChrisGundryCEGA » Thu Jan 26, 2017 10:31 am

Hi All,

We have a new storage appliance and we have setup 3 new ReFS volumes for our backup repos. We have started backups to these new volumes and we are seeing that the space usage on disk does not seems to be as expected. For example, on one of the volumes:
If I select all files on the disk and select properties I get 871GB.
If I right click the volume and check used space I get 975GB.
Shadowcopies is disabled and I have selected all hidden files and system folders when checking properties. There is nothing in 'system volume info' folder either.

The ReFS is formatted with 4k cluster size as that is what was recommended to me previously, but I see current recommendation now seems to be 64k which is slightly annoying as the volumes are now setup.

We are using Veeam 9.5 and the Veeam server and Repo are the same server which is running Server 2016.

We have the same issue with all 3 ReFS volumes. I need to move our backups over to this new storage ASAP but I am very concerned that this space issue is getting worse the more data I put on the volume.

The repo setting to align blocks is selected for some reason, could this have anything to do with it?

Can anyone advise why you think this might be happening?

Thanks!
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Re: Server 2016 ReFS

Veeam Logoby PTide » Thu Jan 26, 2017 11:32 am

Hi,

It's not quite clear where you get that info from, could you provide a couple of screenshots for clarity sake please?

Thanks
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Re: Server 2016 ReFS

Veeam Logoby ChrisGundryCEGA » Thu Jan 26, 2017 11:33 am

I have just re-created one of the volumes with 64k size and re-created the repo without aligning blocks and started a job, which isn't finished yet.

Files are showing size of 45.7GB
Disk is showing 286GB used!!
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Re: Server 2016 ReFS

Veeam Logoby ChrisGundryCEGA » Thu Jan 26, 2017 11:35 am

Screenshot here:
http://imgur.com/dX2PXkd
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Re: Server 2016 ReFS

Veeam Logoby ChrisGundryCEGA » Thu Jan 26, 2017 11:43 am

My thinking being that the size of the files should match the size of the used space. The ReFS and spaceless full backups should actually mean that the space used at the disk level shows less space used than the size of the files shows.

But as we don't have any spaceless full backups yet, the space should just match and be the same, within a small margin to account for the 64k block size and a file that is less than 64k taking up a full 64k. But there is very little data on this volume at present.

Currently it now shows 79GB used in file properties and the disk properties shows 310GB used!
Treesize also only shows 79GB being used.
Treesize also shows 42.6TB free of 42.9TB so again 300GB usage, but not in the Veeam files...??
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Re: Server 2016 ReFS

Veeam Logoby ChrisGundryCEGA » Thu Jan 26, 2017 12:11 pm

I have now stopped the Veeam job and deleted the files but it still shows as 234GB in use. Down from 330GB when I stopped the job...

The difference between 330GB and 234GB is the size of the backup file.

I have now re-formatted the ReFS volume fresh and it imediatly shows as 234GB in use...

Is this some ReFS data taking up a % of the overall size. This volume is a fairly large 43TB, so its about 0.55% of the total being used up.

I re-formatted as NTFS and it shows the full 42.9TB available with no phantom space being used up...

E: drive volume is 8.69TB in size. It is showing 152GB used on the disk but only 73.1GB used in files. 152GB minus 73.1GB gives us 78.9GB. If we work out 78.9GB as a % of the total capacity we get 0.88% which is close to the 0.55% above.

F: drive volume is 15.9TB in size. It is showing 1034.24GB used on the disk but only 936GB used in files. 1034GB minus 936GB gives us 98GB. If we work out 98GB as a % of the total capacity we get 0.64% which is pretty close to the 0.55% above.

Does that make any sense to anyone??
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Re: 2016 ReFS and file allocation size

Veeam Logoby PTide » Thu Jan 26, 2017 2:09 pm

Please check this post for a detailed explanation in regards to ReFS overhead.

Thanks
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Re: Server 2016 ReFS

Veeam Logoby tsightler » Thu Jan 26, 2017 2:57 pm

ChrisGundryCEGA wrote:My thinking being that the size of the files should match the size of the used space. The ReFS and spaceless full backups should actually mean that the space used at the disk level shows less space used than the size of the files shows.

But as we don't have any spaceless full backups yet, the space should just match and be the same, within a small margin to account for the 64k block size and a file that is less than 64k taking up a full 64k. But there is very little data on this volume at present.

Currently it now shows 79GB used in file properties and the disk properties shows 310GB used!
Treesize also only shows 79GB being used.
Treesize also shows 42.6TB free of 42.9TB so again 300GB usage, but not in the Veeam files...??


Did you check the volume immediately after you formatted it? ReFS sets aside a significant amount of space during format, by my observation around one-half of 1% of the size of the volume as reserved space, but it doesn't seem to be completely linear so that's just an estimate. With a 47TB disk that would be almost 250GB shown as used immediately after formatting. 4K clusters set aside more space than 64K clusters, the gap widens as the volume size goes up.
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Re: 2016 ReFS and file allocation size

Veeam Logoby ChrisGundryCEGA » Thu Jan 26, 2017 3:05 pm

I don't know why PTide merged my post with this thread as it doesn't seem to reference anything about the issue I am seeing.

Hi tsightler,

Thanks for your reply which confirms what I have been seeing. Yes, I checked straight after formatting. It's unusual to see it as 'used' space though, rather than usually I would expect to see the overall capacity being lower after formatting, rather than it showing up as full capacity but with some 'used' space.

It seems like I am seeing ~0.5% overhead on 64k and between 0.5 and 1% on 4k block sizes.

Do you know of any documentation that explains what this is and why it happens? I can't seem to see anything!

Dmitriy ahs also just emailed me to say he just replicated the issue in a test environment and confirmed the same ~0.53% lost space... Odd.

Thanks
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Re: 2016 ReFS and file allocation size

Veeam Logoby tsightler » Thu Jan 26, 2017 3:10 pm

It's unusual for a Windows filesystem, it's not that unusual for filesystems on other operating systems.
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