It does not mark where parity data lives it's striped across all drives. Let's illustrate the above picture with an example. Your NAS chassis can hold a maximum of twelve drives. At some point you want to expand.
Furthermore, you can no longer expand your pool, so the remaining two drive slots are 'wasted' 2. You end up with a maximum of ten drives. In this example, to make use of the drive capacity of your NAS chassis, you should expand with another six hard drives. This is illustrated above. Storage-wise it's more efficient to expand with six drives instead of four.
But both options aren't that efficient. Because you end up using four drives for parity where two would - in my view - be sufficient. So, if you want to get the most capacity out of that chassis, and the most space per dollar, your only option is to buy all twelve drives upfront and create a single RAID-Z2 consisting of twelve drives.
Buying all drives upfront is expensive and you may only benefit from that extra space years down the road. So I hope this example clearly illustrates the issue at hand.
With ZFS, you either need to buy all storage upfront or you will lose hard drives to redundancy you don't need, reducing the maximum storage capacity of your NAS. You have to decide what your needs are. This article also got some attention on hacker news. To me, some of the feedback is not 'wrong' but feels rather disingenuous or not relevant for the intended audience of this article. I have provided the links so you can make up your own mind. This article has a particular user group in mind so you really should think about how much their needs align with yours.
No I don't and this is not my intention. I run ZFS myself on two servers. I do feel that sometimes the downsides of ZFS are wiped under the rug and we should be very open and clear about them towards people seeking advice. In the end, you are waisting multiple drives worth of storage capacity depending on the number of drives in your pool. I am sure it can be done better but it works for me.
The script first goes through the list of backup pools and checks if one of them is online I only every have one connected at a time. If it is not online it tries to import the pool, which you need to do after reconnecting the external HDD. I used --no-sync-snap to only sync the existing snapshots and stop it from creating temporary additional snapshots. After the backup sync is done the script will use the prune program to clean up old snapshots on the backup pool.
The current setup will clean up all monthly snapshots older than 16 weeks, all weekly older than 3 months, all daily older than 2 months, all hourly older than 2 days, all frequent ones older than 1 hour and keep all yearly backup snapshots forever.
All the progress and possible errors will written to a log file. You can find it in the path defined at the start of the script. To run this script, just download it from GitHub or copy it from here to a backup. The first run might take quite some time if you have many snapshots, following runs will be much faster though.
Now this script automates the backup process but who automates the script? I still do not want to run the script regularly. Fortunately the system has a build-in solution for this called crontab. You can use that to run any task in a regular interval.
I used this to run my backup script every 30 minutes. If you want to change it just search for a crontab generator and generate your own schedule.
We have a running system with a lot of pretty safe storage. All the data has regular snapshots and is backed up to external disks as well. If you want an even better solution consider also pushing the data in an encrypted format to some web service for a third copy. I might write a future article about this. The setup is simple if you use Ansible.
You will only need a couple of minutes for the manual part of setting up the backup process. Afterwards you only need to switch out the external HDDs from time to time and check the backup logs. Let me know if you are running into any problems with this setup or are missing anything.
In the next blog post s I will describe how I automatically check if I am missing any backups and how I created users and made the files available via the network to other computers. Hosting your own services is pretty simple with Docker.
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You should upgrade or use an alternative browser. Thread starter kbarb Start date Feb 17, Status Not open for further replies. Joined Feb 11, Messages Sorry, I know this has prob. I've read a lot of the ZFS docs and think I have filled in most of the known unknowns, now I'm just wondering about the unknown unknowns, as someone once said. I think I have very minimal requirements. I have on the server box : -- Atom cpu 1. Maybe later, but drives are kind of expensive now after the Thailand flooding disaster.
I guess I get some data integrity but not the redundancy from Raidz1. ZFS really seems like the next great thing, but you know, there's a bit of a learning curve with the adding, removing, replacing, etc.. I'm up for it though, if it's the right way to go. I can't just pull the drives out and attach them to another computer because of the ZFS, right?
So for quick access would the best plan be to have a virtual machine of Freenas on my workstation , which would then be able to import the drives and read them?
It comes with a cost, however. According to this Reddit post by an Oracle employee, the formula for calculating the ARC header mappings is:. So let us make some sense of that for our purposes. This would be a pretty common configuration choice for a lower-end VM storage box.
The above comparison attempts to illustrate this fact. The ultimate goal here is to prevent our pool from having to do as many reads as we can. While the ARC does not directly cache writes, it can speed up your write performance by freeing your drives from having to constantly read from disk.
When a write to disk occurs, it must first pass through system memory where a transaction group or TXG is created. In the event of a crash or a power failure, corruption will have occurred and you will have lost the data being written.
ZFS can also write data blocks synchronously. If the system crashes or its power interrupted, the data will remain in the ZIL. Since system memory is volatile, and our ZIL is not, this can be considered an insurance policy for our write commits. The speed of your writes, however, is now tied to the speed of your ZIL.
By default, the ZIL lives in your pool, but in a logically separate place. It is only ever read from in one scenario. If there was a crash or a power failure. Every time your system is restarted it has to re-import your ZFS pool before proceeding. If there was, that means there were writes that had not yet been committed to disk. It will then read that data and commit it as a new TXG to your pool.
What this all means is that with a sync write, your data is written to the disks in your pool twice. This is called a write amplification , and it will slow any write commits to your pool to a crawl.
Sync writes have a high cost, cutting your write performance in half or more. Having separate hardware prevents the write amplification effect on your pool. It also allows you to put the ZIL on a much faster device. That is important because your writes will still be limited by the speed of your SLOG.
It is for that reason that we recommend Intel Optane for use when sync writes are a requirement. If you feel your data is sensitive enough to require sync writes, buy a SLOG. We have spent some time in this article discussing the key concepts surrounding ZFS. We hope that we have helped provide to provide the necessary knowledge and references to get you started in the world of ZFS.
When you go to build a lab, or when you go out to bid for a new storage solution, the Open Source is a tremendous resource that should be considered. We have not covered everything in the piece.
Special Allocation Classes are an OpenZFS feature, and they allow you to accelerate metadata on your spinning drives with flash storage. Additionally, you can use them to get a better-performing deduplication. This is still a new feature in OpenZFS we have not yet tested or vetted for their viability or value. Additionally, ZFS does on-the-fly compression, has native encryption support, and a whole-host of new features are actively being developed.
We hope to follow this introduction to ZFS piece up with more content in the future around ZFS as new things come about. The calculation mistake scared me too! And another vote for replacing the picture of the EFAX drive with one that people should actually use. Excellent article! It has been perfectly reliable through many power failures and a disk failure. And I have had to pull files from snapshots on many occassions to address user errors.
You mention the performance degradation as the disk fills and files get fragmented. Is there a defragment command to address that? But maybe my knowledge is outdated. Create a new vdev with the new disks, and add this vdev to the existing pool. Perhaps you got confused about vdev vs.
The only way to expand the capacity of an existing vdev itself is to swap all the drives in a vdev with drives of larger capacity; which, while possible, is most probably not the best way to expand the capacity of your pools.
I would love to see the followup article on performance tuning ZFS if you are willing to make it as detailed as this one was.
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