LTO6 performance poor on first write pass?

Am 27.01.25 um 15:26 schrieb Philip Pemberton via Bacula-users:
> Hi all,
>
> This isn't specifically a Bacula question but I know a bunch of you are running LTO drives and I hope you'll grant me the wisdom of your experience!
>
> I'm seeing an unusual (to me) issue with a new-old-stock IBM drive and tapes. They came as a package deal. The drive has about 600 power-on hours and about 40 media-movement hours.
>
> What I'm seeing is that tapes don't write at full speed on their first pass through the drive. I can hear the drive stopping and starting as it writes to the tape.
>
> Sometimes the drive partially ejects the tape and reloads it.
>
>
> The data flow is:
>
>   * NVME disk (hdparm -tT speed = 2254MB/s buffered, cached ~10x faster)
>   * zstd -T0 --fast
>   * mbuffer -t -M 2G -L -s 262144 -P 80 -f -o /dev/nst0
>
>
> When the drive stalls, Mbuffer reports that the buffer is full to capacity and a zero write rate to the drive -- it seems like the drive's buffer is full and it isn't actively writing.
>
> If I pull the error correction logs with smartctl on the sg device, I see 25 write errors corrected in about 35GB of data.
>
>
> I figured I had some bad tapes, but here's where it gets weird.
>
> If I write to the same area I just wrote, the tape writes at about 85MBytes/sec. Not the 150-160MByte/sec the drive should be giving, but still better than the 35MB/s average from the first pass.
>
> I've tried a cleaning tape, this made no difference. The drive isn't requesting cleaning either.
>
> The tapes are Quantum branded Barium Ferrite tapes, which I gather are the same as the IBM branded BaFe tapes I'm using in another drive.
>
>
> Does anyone have any idea what's going on here, and is it expected behaviour for the first write pass on a new-old-stock tape?
>
> Is the time these tapes -- or the drive -- spent on the shelf likely to be relevant? That is to say, if I bought a box of brand new tapes from a channel distributor, are they likely to behave any better?
>
>
> I should note that the tapes I've written read back fine, the drive doesn't report any read errors that I've noticed.
>
> Thanks.

Please try https://www.ibm.com/search?lang=en&cc=us&facetTabs=fixes&origin=fc&q=ITDT&tabType[0]=support

Regards
Udo

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