File to Tape takes more space as expected?

[Vodochnik]

Hi dear community,
please help me to understand, why my backups do not fit on tape (if a little bit bigger then in provided case).

Log: 192.168.106.66\Backup\Off-Site\Agent.Off-Site.TapeFilesBackup.TapeHost.log


[27.03.2025 06:46:22.286] < 6236> mt | Last sessions:
[27.03.2025 06:46:22.286] < 6236> mt | Session: Full backup set 26.03.2025 19:13:24, mediaSeqNumber: 1, sessionNumer: 3, pba: 3121201, directories: 4, files: 22, writeDate: 2025-03-26T18:13:24, Size of files: 10640797057024
[27.03.2025 06:46:22.286] < 6236> mt | Session: Full backup set 26.03.2025 18:35:41, mediaSeqNumber: 1, sessionNumer: 2, pba: 947895, directories: 1, files: 2, writeDate: 2025-03-26T17:35:41, Size of files: 569717862400
[27.03.2025 06:46:22.286] < 6236> mt | Session: Full backup set 26.03.2025 18:20:47, mediaSeqNumber: 1, sessionNumer: 1, pba: 3, directories: 1, files: 5, writeDate: 2025-03-26T17:20:47, Size of files: 248482942976

Total size of files: 10640797057024+569717862400+248482942976=11458997862400 bytes


Log: 2025-03-28T163812_VeeamBackupLogs\veeam1\Backup\Off-Site\Job.Off-Site.TapeFilesBackup.log

[27.03.2025 06:46:26.575] <01> Info (3) [Tape HAI023L8] Updating, Capacity 11999999164416, Remaining 20526923776, PartitionCount 1, IsWriteProtected False, IsWorm False, UsageStatistic {LifetimeRead: 12018MB, LifetimeWritten: 10952693MB, LoadCount: 3, CleaningCyclesLeft: 0}

Bytes written: 11999999164416-20526923776 = 11979472240640 bytes written (capacity - remaining)

Written to tape minus total size of files = 11979472240640-11458997862400 = 520474378240 bytes, 485GB space wasted on L8 tape?!
Somehow is it too big overhead, isn't it? What am I doing wrong?

Case #07654603

[david.domask]

Hi Vodochnik,

Looks like the case was just opened, and Support has not had a chance to review the logs yet, so let's wait for their analysis.

I would trust the capacity stats from this line:

[27.03.2025 06:46:26.575] <01> Info (3) [Tape HAI023L8] Updating, Capacity 11999999164416, Remaining 20526923776, PartitionCount 1, IsWriteProtected False, IsWorm False, UsageStatistic {LifetimeRead: 12018MB, LifetimeWritten: 10952693MB, LoadCount: 3, CleaningCyclesLeft: 0}

That will show how much was actually left on the tape, and looks like it's about 20 GiB left:

PS /Users/vvvvvv> 20526923776/1GB
19.1171875

How to explain this? Regrettably can only guess right now but it's possible there are issues when writing to tape and the tape drive has to scroll ahead to section of the tape; this is how tape handles such recoverable write errors, it just moves down the track and continues, and returns offsets from the successful write to the client, meaning that unsuccessful writes are dead space on the track.

I am simplifying this a little, and remember this is just a guess, but it would explain the behavior.

I would wait for Support's analysis of the logs first to get an idea what's happening, maybe they'll see the same or another behavior that explains what you're seeing.