Ubuntu server inquiries and application for the mentoring program

[Seth Arnold]

On Fri, Apr 22, 2016 at 08:15:13AM +0800, Juan Karlo de Guzman wrote:
> Moving forward, I was just wondering if you guys can help me out
> utilizing the new technology that is natively supported when Ubuntu
> 16.04 was released. It is the ZFS file system. That term is familiar for

ZFS is an amazing tool. To get the most benefit it's worth investing a few
hours of reading; I suggest starting with the excellent series of blog
posts by Aaron Toponce;
https://pthree.org/2012/12/04/zfs-administration-part-i-vdevs/

I've got some advice, probably duplicates much of what's in the best
practices pages:

- Do not use dedup

- Turn on lz4 compression for the top-level dataset when creating the
  pool, so all datasets get it by default

- raidz1, raidz2, raidz3 are good for bulk storage but slow

- mirrors are faster than raidz*, but also more expensive per terabyte

- if you set ashift=12 now, even on 512byte hard drives, you'll be able to
  replace the 512byte drives with 4k drives in the future without
  performance loss. (ashift=12 apparenlty interacts poorly with raidz*.)

- You cannot remove a vdev from a pool. Do not make mistakes with "zpool
  add". I've known five or six people who've accidentally added a single,
  bare, drive to their pool, turning it into roughly a raid0. The way out
  is to destroy the pool and recreate it from your backups.

- If you're using 2tb drives or larger, it's really worth using raidz2 or
  raidz3, or three-way mirrors. Resilvering takes long enough.

- Do not use dedup

There's some details specific to Ubuntu's ZFS:

- Ubuntu currently doesn't support root-on-zfs. This is a huge amount of
  work for a distribution to support, so I'm not surprised it didn't
  happen for 16.04 LTS. I recommend skipping it yourself, though I
  understand Richard Laager is preparing a HOWTO that may be useful if
  you want it anyway.

- Ubuntu currently doesn't ship a cronjob or systemd job to schedule
  scrubs periodically. You really should do one yourself in the meantime.

- Ubuntu currently doesn't ship a cronjob or systemd job to schedule
  snapshots. There's a lot to know about snapshots, so it's worth
  investigating tools that schedule snapshots automatically.

It's truly astonishing what ZFS can do for you. In five minutes I was
able to assemble nine 3TB drives into three 3-way mirrors for a total
of 9TB of storage space, excellent redundancy, and excellent throughput
that rivals consumer SSDs with large enough operations, compression,
and checksums. All this is before using a l2arc or slog device to push
speeds through the roof.

> server has less than 4 GB of RAM then a 32-bit version of the server
> should be used so that the memory won't be entirely wasted. Although,
> feel free to correct me if I'm wrong.

While it's true that 64bit systems on small memory VMs is slightly
wasteful with pointer sizes, I think the benefits of 64 bit systems
outweighs the downsides in almost all cases:

- more CPU registers are free for use
- more CPU instructions are available for more effecient use of data
- better address space layout randomization makes certain kinds of attacks
  far less likely to succeed.
- If all instances in your organization are 64 bit, your squid-deb-proxy
  or similar tools will have better hit rates with less storage.


Have fun with your new toys :) I sure am.

Thanks
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