Re: [gentoo-user] NAS and replacing with larger drives

[Frank Steinmetzger <Warp_7@gmx.de>]

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Am Sun, Dec 11, 2022 at 08:44:42AM -0700 schrieb Mark Knecht:

> Also, I think there are ways for you to build complex pools like a RAID0
> from your 6TB and 8TB drives, and then a RAID1 using the RAID0 and your
> 14TB drive but I've never tried it because mine don't have enough drive
> slots for that.

After a longer fruitless search on the interwebs (I ddidn’t want to start up
my NAS just to check this) I finally found the right search keywords and
found a reddit thread about that. And it even throws LVM into the
discussion. ^^
https://www.reddit.com/r/zfs/comments/fitc73/raidz_with_nested_vdevs/

Also <https://zfs-discuss.zfsonlinux.narkive.com/g2THW8n4/nested-vdevs>:
“Here's a definitive answer from the man page for zpool.

Virtual devices cannot be nested, so a mirror or raidz virtual device can
only contain files or disks. Mirrors of mirrors (or other combinations) are
not allowed.”


I would advise against a JBOD pool anyways. Because if one drive dies, the
whole JBOD is gone. That goes for ZFS and probably for LVM, too (though I am
not sure how writes are distributed across JBOD disks). If the goal is
redundancy, you could buy a second drive to match the size of an existing
one and build a mirror. If redundancy is not a goal, then use the drives
separately like you do now. If one fails, then only its content is gone (or
even just the files sitting on the broken sector).

> Also, turn on compression. It saves me between 15-20% so 14TB becomes 16TB
> storage. YMMV. Video files don't compress, at least not much. Data files
> generally do.

It doesn’t hurt to switch it on, especially with lzo. But with video, the
benefit will be negligible. When storing a block of data (a “record” in ZFS
speak), it is passed through the compressor and only if the compression gain
is above a given threshold (10 % methinks), the block is written to disk
with compression.

What is more relevant in filesystems for big files (i.e. videos): set the
record size to 1 MB. The default is 64 kB, IIRC. Each record requires one
block of metadata (which includes the record checksum). So bigger records →
fewer meta blocks → better storage efficiency.

If you use big records for small files, then efficiency goes down a little.
It’s a similar (but a little more complicated) principle as when you write a
100 byte text file to a file system that uses 4 kB clusters. That file will
still use up 4 kB on disk.

The record size can be set per-dataset. So in your pool you could create a
dataset with a smaller record size for office documents, images and music,
and another dataset just for videos.

> Hope this helps. I think you'll find TrueNAS fun actually but there is a
> learning curve. I've used it for about a year and barely scratched the
> surface.

The main reason for me why I would wanna use it as opposed to a standard
Gentoo install: the OOTB web interface to manage all sorts of accounts,
access and permissions under one nice hood.

-- 

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