Should I use a CoW filesystem on my PC if I only wanted snapshot capabilities ?


 
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Top Forums UNIX for Beginners Questions & Answers Should I use a CoW filesystem on my PC if I only wanted snapshot capabilities ?
# 15  
Old 03-11-2020
Two more comments on zfs:
  • Don't fill up the filesystems
    If you fill up zfs file systems above 80%, performance will degrade.
  • No manual balancing method available
    If you have a Volume with more than one vdev and they are not equally full performance also degrades. For best performance vdev utilization should be equal of every vdev. But there are times when vdev utilization is completely different. For example if you add a new vdev: The new vdev will be empty. There are 2 typical ways to solve that:
    • utilization will slowly level to the pool average over time
      The percentage of the probability for a vdev to be the targe for a new write is the reversed percentage of the utilization of that vdev. So the least filled up vdev will get more new data as the other ones and the vdev utilization will average with writes and deletes over time.
    • export and import the zfs pool
      If you like to have it immediately, you may export and import the pool. That way on the import all data will be distributed evenly over all vdevs. That task of course needs a lot of temporary space and probably time when you have quite some TB of data.

Regarding the performance of filesystems, I'm interested in it quite much. Right now, I'm writing benchmark scripts testing different aspects of it and will open a thread here soon.
# 16  
Old 03-11-2020
Quote:
Originally Posted by stomp
Encryption makes the backup task more difficult.
Unfortunately I need it, I can't avoid it.

Quote:
Originally Posted by stomp
Since you're a beginner, a CloneZilla can be a fallback solution until you're famillar enough with your linux os. With CloneZilla you can save and restore the os partition without knowing very much about linux.
Okay Clonezilla is not an option for me. Simply because I don't have that much of space to spare. It seems I am not getting the answer that I want because I am not asking the right questions.

So let me apologize for that, and let me ask if the following workflow is possible on Linux.
  1. I have a single 1 TB SATA hard disk.
  2. I will be using an encrypted LVM with ext4 formatting.
  3. Now lets say before an update or a dist-upgrade I take a snapshot of the root partition and store that snapshot in the root partition itself.
  4. The upgrade or update fails or is causing problems, and the system is no longer bootable to my desktop.
  5. I boot into a live CD.
  6. Mount my encrypted partitions, and /proc, /sys and /dev from the live CD.
  7. Chroot into my system.
  8. Find the saved snapshot.
  9. Revert it.
  10. Exit from Live CD environment and boot back to the reverted system.

Main Challenges:
  1. Will the backup process work ?
  2. Will the Live CD of my OS contain CLI tools to decrypt encrypted partitions ?

As you can see, I cannot forego full-disk encryption nor do I have that much space or time for a full cold boot snapshot of a partition.

So is the above workflow possible ?
# 17  
Old 03-12-2020
Quote:
So is the above workflow possible ?
From all my experience in linux I would assume yes. The better OSS pieces can be operated from rescue systems. But since I have very little competence in the area of those encryption techs, I can not help you further here.
# 18  
Old 03-20-2020
Hi,

I just had a use case for encryption. I decided to use dm-crypt to create an encrypted container. It's fairly easy. You may just have an encrypted container for your live data and another for your backup. Once it is open, you can read from and write to the filesystem. Many rescue distributions support dm-crypt out of the box(grml, sysresccd, knoppix).

Interesting would be, how you securely automate that, because a backup that's not automated is worthless for me. And if you do not do it securely, encryption makes no sense in my view. Maybe you can place a pendrive with the key on it in your computer, so it only boots up when the pendrive is there?

Here's a tutorial for you to read(use google for a lot of resources on the dm-crypt topic):

How To Use DM-Crypt to Create an Encrypted Volume on an Ubuntu VPS | DigitalOcean

Interesting would be, what the nature of your data is and what confidentiality level of your data is, so I/we can better understand your situation and maybe help more.

regards,
stomp.

Last edited by stomp; 03-20-2020 at 12:25 PM..
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