Your choice. You can obviously adjust this formula for larger or smaller! The important concept here is the idea of breaking mirror vdevs using zpool detach, and creating mirror vdevs from single-disk vdevs using zpool attach. Mercenary sysadmin, open source advocate, and frotzer of the jim-jam.

zfs mirror

View all posts by Jim Salter. Thank you for this guide, very informative. Third off-topic : Is there any usecase where it would make sense to NOT have an entire disk as a vdev? Assume no-one accesses both partitions at once, the performance hit would obviously be bad otherwise.

Zpool split is for maintaining a copy of the current pool on the detached disks. Very limited use-cases, but yes. Your email address will not be published. Currently you have JavaScript disabled.

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Bad Behavior has blocked access attempts in the last 7 days. Skip to content About Contact. Step one: create the new pool, copy data to it First up, we create a simple temporary zpool with the two available disks. Step two: scrub the pool Do not skip this step! Step five: scrub tank, destroy temp Do not skip this step. Published by. Jim Salter Mercenary sysadmin, open source advocate, and frotzer of the jim-jam.

Hi Jim, Thank you for this guide, very informative. Best regards, Jarek. Leave a Reply Cancel reply Your email address will not be published.

zfs mirror

Next Next post: When static routes on pfSense are ignored.A pool is a collection of vdevs. The pool itself will distribute writes among the vdevs inside it on a relatively even basis. If you put the same drives in a zpool as two mirror vdevs, they will be a 2x2TB mirror and a 2x1TB mirror, and your after-redundancy storage will be 3TB. If you keep writing to the pool until you fill it, you may completely fill the two 1TB disks long before the two 2TB disks are full.

What if you have twelve disks, and you configure them as two RAIDZ2 dual parity stripe vdevs of six disks each? Well, your pool will consist of two RAIDZ2 arrays, and it will distribute writes across them just like it did with the pool of mirrors. Again, they go in the pool, the pool distributes writes across them. This is where a lot of people get themselves into trouble. Be careful here.

Keep in mind that if any single vdev fails, the entire pool fails with it. There is no fault tolerance at the pool level, only at the individual vdev level! So if you create a pool with single disk vdevs, any failure will bring the whole pool down. And you have no fault tolerance at all until the disk has been replaced and completely resilvered… which could take days or even weeks, depending on the performance of your disks, the load your actual use places on the disks, etc.

This sucks. Conventional RAID5 is strongly deprecated for exactly the same reasons. Problem solved, right? Well, problem mitigated — but the degraded performance and resilver time is even worse than a RAIDZ1, because the parity calculations are considerably gnarlier.

ZFS: You should use mirror vdevs, not RAIDZ.

And it gets worse the wider your stripe number of disks in the vdev. Saving the best for last: mirror vdevs. When a disk fails in a mirror vdev, your pool is minimally impacted — nothing needs to be rebuilt from parity, you just have one less device to distribute reads from. In no case are you re-writing entire stripes, all other vdevs in the pool are completely unaffected, etc.

Mirror vdev resilvering goes really quicklywith very little impact on the performance of the pool. This assumes two disk vdevs, of course — three disk mirrors are even more resilient. Because of the drastically shorter time to resilver, and drastically lower load placed on the pool while doing so.

ZFS is awesome. But there are still lots of potential ways for your data to die, and you still need to back up your pool. For even better performance, consider using mirroring. Please read that last bit extra hard: For even better performance, consider using mirroring. Now what? Well, you actually can upgrade that original RAIDZ2 of 1TB drives — what you have to do is fail one disk out of the vdev and remove it, then replace it with one of your 4TB drives.

Wait for the resilvering to complete, then fail a second one, and replace it. Question is, how long did it take to do all that resilvering? You might manage to get six resilvers done in six full days, replacing one disk per day. But it might take twice that long or worsedepending on how willing to hover over the system you are, and how heavily loaded it is in the meantime. So you did give up a terabyte there.

Maybe since you only needed to put in two more disks to get more storage, you only bought two 2TB drives, and by the time you were feeling cramped again the 4TB disks were available — and you still had four bays free. You do it the same way — you replace, resilver, replace, resilver — but this time, you see the new space after only two resilvers. So you can probably upgrade an entire vdev in a single day, even without having to hover over the machine too crazily. The performance on the machine is hardly impacted during the resilver.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

Server Fault is a question and answer site for system and network administrators. It only takes a minute to sign up. The hardware I'm looking at includes 2x 4-port SATA controllers, 2x small boot drives one on each controllerand 4x big drives for storage. This allows one free port per controller for upgrading the array down the road. Where I'm a little confused is how to setup the storage drives. For performance, mirroring appears to be king.

The other thing I'm trying to wrap my mind around is the benefit of mirrored arrays with more than two devices. The simple answer is that to mirror something takes almost no processing power - it just writes to the disk a second time.

Mirroring is always the preferred solution for high-speed data, if it's just bulk-storage without fast write speeds, RAID-Z2 is a good alternative that does allow any two drives to die as you allude to. The other advantage is that mirrored pools can be expanded with more mirrored devices - while a RAID-Z2 can not be expanded - though more RAID-Z2 storage can be added to the pool, it will be two RAID-Z2 storage pools concatenated in effect rather than equally split between all the storage and striped.

Also, remember that RAID is a fault-tolerance solution. You don't implement RAID-Z2 to protect against data loss -- you perform backups or replicate to do that. RAID-5 to keep your systems operational in the event of hardware failure.

Sign up to join this community. The best answers are voted up and rise to the top. ZFS: Mirror vs.

zfs mirror

Asked 11 years, 1 month ago. Active 8 years, 1 month ago. Viewed 20k times. John Clayton John Clayton 1 1 gold badge 6 6 silver badges 10 10 bronze badges. Active Oldest Votes. Does it provide any additional data integrity beyond what ZFS already provides?

Or is it simply needed for any two drives to die?What's new New posts New resources Latest activity. Resources Latest reviews Search resources. Log in Register. Search titles only. Search Advanced search…. New posts. Search forums. Forum Rules. Log in. Register Now! Register for the iXsystems Community to get an ad-free experience and exclusive discounts in our eBay Store. JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.

zfs mirror

Thread starter jgreco Start date Jun 11, Status Not open for further replies. Joined May 29, Messages 12, ZFS is a complicated, powerful system. Unfortunately, it isn't actually magic, and there's a lot of opportunity for disappointment if you don't understand what's going on.

ZFS will allocate long, contiguous stretches of disk for large blocks of data, compressing them, and storing the parity in an efficient manner. RAIDZ makes very good use of the raw disk space available when you are using it in this fashion. In order to store that, you store the 8K data block, then three additional parity blocks It's exhibiting the speed of a single disk.

The solution to this is mirrors. First, mirrors do not consume a variable amount of space for parity. Second, you're likely to have more vdevs.

That 12 drive system we were just talking about will have 4 three-way mirrors or 6 two-way mirrors, which is 4x or 6x the number of vdevs. This translates directly to greatly enhanced performance! Another substantial performance enhancement with ZFS is to maintain low pool occupancy rates.

It's a combination of fragmentation and occupancy that causes performance to suffer. For mirrors, this is also true, but because the data being stored is often VM disk files or database files, it becomes more complicated.

Because it is a copy-on-write filesystem, rewriting a block in a VM disk file causes a new block somewhere else to be allocated, and creates a hole where the old block was, when that block is freed after any snapshots are released, etc. When writing new data, ZFS likes to allocate contiguous regions of disk to write its transaction groups. An interesting side effect of this is that if you are rewriting VM disk blocks 1, andthese may actually be written as sequentially allocated blocks when ZFS dumps that transaction group to disk.PhD from Cornell.

Lately I have been performing upgrades to the hard drives in my computers. It provides a lot of really attractive features for providing redundancy in your data. So why setup a ZFS mirror? Once setup, if we lose a disk due to hardware failure the pool will still run in a degraded state, giving us time to swap in a new drive.

The two HDDs are different capacities. This gives us two empty 2TB drives to create the mirror on. Install how you want, but I use yaourt :. The kernel modules for ZFS are tied to a specific kernel, which required a downgrade for me at the time I installed. Once you exit dependency hell zfs will be installed. Something I learned about while setting this up learning new things is another large part of the motivation for me here is Advanced Format drives.

Older drives will store data in byte sectors. Fortunately, I found this pdf model number format guide which details the letters in each model number. So, can we mix the two? Several people on a few forums suggest forcing the 4K sectors when mixing drives, as not much performance is lost in forcing byte sectors to align to byte sector, but there is definite performance lost the other way.

I wiped the data off my old drive and so both drives are unformatted i. To see all your drives we can use parted. Datasets allow you to do such things as setting disk usage quotas and maintaining individual snapshots per dataset. The first of which will be auto-mounting at boot. The zfs daemon is capable of loading a zpool and mounting it at boot. In order to do this we need to setup a cache file, then enable the zfs daemon. You can check out your new zpool with a simple zpool status :.

Then all we need to do is rsync our data to our home directory from our backups and enjoy the new disk redundancy. I really setup this pool about a month ago. There are many more things you can and should do with your zpool, such as having automated snapshots and scrubbing your zpool regularly. Setting all these things up at once takes a while on the first time through, and I was planning on including it all in this post.

As a result, this already lengthy post was becoming way too long. So expect to see more ZFS related posts in the near future. A quick guide to setting up Pi-hole on a virtual machine provisioned with vagrant. Rather large, somewhat unorganized, photo gallery from my trip to Japan in July.Trail BlazersThe Trail Blazers, off since Tuesday, have a three-game losing streak, with Saturday's game completing a four-game homestand.

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FreeNAS - ZFS Pools Overview

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Rebalancing data on ZFS mirrors

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