First Light: Balkonsternwarte

First Light: Balkonsternwarte

Ein Balkon mit Südblick ist eine tolle Gelegenheit für astronomische Beobachtungen. Wenn dann auch noch die Sicht nach Norden und auf den Polarstern frei sind, gehört auf den Balkon selbstverständlich ein Teleskop zur Himmelsbeobachtung.

Den Traum einer kleinen Balkonsternwarte habe ich mir nun erfüllt. Da größere Optiken und Brennweiten mitten im Stadtgebiet eher nicht in Frage kommen und ich mit den Skywatcher Montierungen ganz gute Erfahrungen gemacht habe, fiel die Wahl auf die Skywatcher HEQ-5. Zusammen mit einem Leitrohr und M-GEN Autoguider, einer bereits vorhandene Canon 40Da und einigen EF Objektive sowie einem Haufen Zubehör, waren im Dezember ‘17 endlich alle notwenigen Teile beschafft.

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ZFS: auto-snapshots and Windows shadow copies with Samba

ZFS: auto-snapshots and Windows shadow copies with Samba

With ZFS snapshots and Samba’s shadow_copy2 module, you can expose snapshots to Windows clients as shadow copies.

First, install zfs-auto-snapshot on Debian:

apt-get install zfs-auto-snapshot

Default configuration for zfs-auto-snapshot uses specific labels like daily, weekly etc. This is incompatible to samba’s expected snapshot format. As a good workaround, instead of using text labels, I’ve changed the labels to numbers:

31: for daily snapshots
05: for 5 minute interval snapshots
24: for hourly snapshots
12: for monthly snapshots
52: for weekly snapshots

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ZFS: txg_sync stuck at 100% while copy large dataset with rsync

ZFS: txg_sync stuck at 100% while copy large dataset with rsync

While transfering a large dataset (2TiB) via rsync from ext4 to zfs, rsync hangs at some time and txf_sync stuck at 100% cpu.

It was a fresh system and zfs was set up just a few minutes ago. After some research, I found out that this problem is related to ARC.

I’ve changed the zfs_arc_min parameter while trx_sync stuck and the system immediately responses.

echo 1073741824 » /sys/module/zfs/parameters/zfs_arc_min

This sets the minimum size (hard limit) for ARC to 1 GiB.

References

https://github.com/zfsonlinux/zfs/issues/3409#issuecomment-283551036

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ZFS: Create pool with missing devices

ZFS: Create pool with missing devices

ZFS on Linux has no support for creating pools with missing vdevs. Thats a benefit of mdadm which accepts a missing keyword in a list of devices.

But there is a workaround:

First, check the size of an existing device (all devices must have same size). In my case, each disk has 2000398934016 bytes. I’ve used fdisk to check the size but you can use whatever you want.

Now create parse file(s) with the given size.

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ZFS: Why is L2ARC hit ratio so low?

ZFS: Why is L2ARC hit ratio so low?

Using an additional SSD disk as a second level cache for ARC - called L2ARC - can speed up your ZFS pool. But if you analyze how often the cache is used you find a very low hit ratio. To understand why the hit ratio is low you should know how the L2ARC works.

ZFS uses a primary cache - the ARC - which takes some space of your available RAM. Until the ARC is really full, no noteworthy data is written to the L2ARC. Thus, until the ARC cache is warm, the L2ARC cache isn’t used. But even it is not used, a read request triggers a lookup in ARC and then in L2ARC. Because both caches are cold after a reboot, you can see a lot of cache misses.

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