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FreeNAS: Open Source Storage Operating System

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Re: FreeNAS: Open Source Storage Operating System

#41

Post by cbsmith »

allendoerfer wrote: post #32

Storage is a really weak area of mine, but it is important, and I do not see much technical discussion here anyway, so I am going to expose myself: How does integrity protection work in practice? I know that the bits on the HDD itself do not map one to one to bits you can actually use and that it uses that to protect us from flipped bits. I know that beyond that RAID/RAIDZ is supposed to help. I guess redundancy alon…

So many levels to this. Drives themselves remap sectors to handle bad sectors, and some have integrated ECC bits... there are also things at the sensor level to help recover from errors. Once you are at the block level, you have simple parity checking with some redundancy models, but the good ones use ECC bits. Usually this is done at the block device layer, but ZFS and some other filesystems do this at the filesystem layer (sometimes you have multiple layers of this). You're right that beyond a few copies, the main win tends to be read speed, but there is one other factor: surviving rebuilds. As drives get larger, the failure rate is such that the chance of failure during a rebuild gets too disturbingly high, so you need additional redundancy to avoid catastrophic failure during recovery.

As for "automatically fix it", the short answer is there is a lot of stuff that automatically fixes problems, but it is a leaky abstraction. RAID-5 rebuilds are notoriously terrible for performance, and often it is easier to have logic for dealing with failures & redundancy at the application layer.

FreeNAS and similar projects are definitely intended to be turnkey storage solutions. They have their strengths & weaknesses, but the notion that you just plug it in and go isn't too far off. Usually you don't go with the blinky light, but with an alerting mechanism (e-mail, SMS, whatever) that you integrate with it for notifications about problems. In principle, it is a fire & forget kind of thing.

Re: FreeNAS: Open Source Storage Operating System

#42

Post by [deleted] »

tobias3 wrote: post #37
benologist wrote: post #28

Earlier quoted context omitted.

Your link is people complaining that the source isn't being released fast enough ... and Synology has told them it will be put on SourceForge when they're ready. There seems to be a lot of precedent for that to go how they said it will. There's also an independent community that facilitate installing and using it on your own hardware including the latest version that's still waiting on the source dump.

Sure, no one needs that source code anyway because they are not adding anything of value. But if they are not complying the GPL license they are legally not allowed to use the GPL projects. As an example for their relationship with upstream, they market the btrfs feature ( https://www.synology.com/en-global/dsm/Btrfs ) but don't have anyone working on btrfs (and btrfs could surely need the help). I can see one patch…

[deleted]

Re: FreeNAS: Open Source Storage Operating System

#43

Post by wilhil »

I have bad memories of freenas (before the split/new version) many years ago when I had a disk and power failure... hdb went, so, c/d moved up a letter and it automatically screwed up raid...

... I was able to recover, but, I remember how many hours I spent on it.

Please tell me it is better now?

Re: FreeNAS: Open Source Storage Operating System

#44

Post by Nacraile »

allendoerfer wrote: post #39
Nacraile wrote: post #36

Earlier quoted context omitted.

RAID generally does not protect against bit-rot (i.e. undetected errors); it only protects against detectable errors / catastrophic disk failure. ZFS does protect against undetected (at the disk level) errors. To a first approximation, it does this by keeping block checksums alongside pointers so that it can verify that a block has not been changed since it was referenced, by keeping multiple checksummed root blocks,…

> Naturally, there are information-theoretical limits to the number of corruptions that may occur for detection/correction to be guaranteed. To my practical point: Does it tell me, when it approaches that limit or do I have to put in more maintenance? Can it be fixed by swapping one of the drives?

The limits are on the number of simultaneous failures. Data is safe provided that too many errors do not accumulate before they can be detected and corrected. This is fundamental fact: no real storage system can tolerate an unbounded number of simultaneous errors without an unbounded number of space for replicas. You can control the number of allowable simultaneous errors by tuning redundancy settings (the trade off is space efficiency vs. probability of data loss). It is straightforward to put in place an automated process to guarantee that errors are detected within some finite period of time.

Re: FreeNAS: Open Source Storage Operating System

#46

Post by ultramancool »

jzelinskie wrote: post #21
tracker1 wrote: post #8

Although I don't think I'd ever DIY another NAS box, I would suggest the following, use a common chipset controller that exposes each drive/device separately with all information, some don't. Also, prefer a system with ECC, Asus supports ECC on most AMD FX supporting motherboards for the less expensive option there. Also, have 2 spare drives on hand. I went back to Synology after my uper-nas crashed and burned (reall…

I wanted to do something like this, but after reading about the failure rates of drives and raid, once one disk fails, it seems like you're fucked. Anybody got some stories or numbers that prove that while repairing my raid for one disk failure I won't just destroy the rest of my drives?

> I wanted to do something like this, but after reading about the failure rates of drives and raid, once one disk fails, it seems like you're fucked. Anybody got some stories or numbers that prove that while repairing my raid for one disk failure I won't just destroy the rest of my drives?

Yeah, I've recovered several failed drives without issue, even on LVM systems where some partitions failed because they were striped but others worked because they were mirrored. No real issues overall.

The only case where you might run into problems is when you get conflicting data between 2 drives, but I've never seen that happen in the real world. Some people will scare you into thinking that happens often but it hasn't been my experience. Often one drive just goes kaput completely or has an entire section which is completely unreadable or extremely slow, for which recovery is just a matter of marking that drive offline, swapping a new drive in and telling it to rebuild. The only case in which you lose everything is if you use RAID0. If you can do RAID10 that's the way to go IMO.

RAID5 can be a little riskier because if one drive is damaged and one fails then you can wind up losing the bunch, but I use it on my personal NAS because it's mostly just TV and the important stuff is syncthing'd to my other machines. Regular scrubbing prevents these issues usually.

Re: FreeNAS: Open Source Storage Operating System

#47

Post by BrainInAJar »

wilhil wrote: post #43

I have bad memories of freenas (before the split/new version) many years ago when I had a disk and power failure... hdb went, so, c/d moved up a letter and it automatically screwed up raid... ... I was able to recover, but, I remember how many hours I spent on it. Please tell me it is better now?

it's ZFS backed, screwing up the RAID is going to be pretty close to impossible.

you can lose the system disk (usb key) that holds your settings, but the data you actually care about will be safe.

Re: FreeNAS: Open Source Storage Operating System

#48

Post by ta_donk_gt »

tracker1 wrote: post #8

Although I don't think I'd ever DIY another NAS box, I would suggest the following, use a common chipset controller that exposes each drive/device separately with all information, some don't. Also, prefer a system with ECC, Asus supports ECC on most AMD FX supporting motherboards for the less expensive option there. Also, have 2 spare drives on hand. I went back to Synology after my uper-nas crashed and burned (reall…

I had a similar bad run with Seagate 3TB drives..3 out of 4 in 2 years. I was really thinking it was the NAS, but switched to WD Reds and have had no issues in 18 months.

Re: FreeNAS: Open Source Storage Operating System

#49

Post by c0g »

ultramancool wrote: post #14
c0g wrote: post #3

I've been using Unraid for a few months. It has a different - arguably inferior - parity strategy but has amazing support for VMs. I've got my gaming machine, my GPU dev box and a bunch of smaller services all in the same box and can do some really sweet online configuration.

How is it for gaming? I'd imagine it's using a VM solution (Xen HVM or KVM so it can do IOMMU?). I've been avoiding it because I figure that VM solution would get detected by anti-cheat in many games (particularly the nasty kernel level ones like EasyAntiCheat, GameGuard, etc).

I have 8x2.8 ghz Xeon cores 32 GB of RAM and a 970 GTX in my gaming vm. Works perfectly for DOOM, Witcher 3, all at 1920x1080 on high settings (maybe not full but damn pretty). Consensus on the forum seems to be you lose low single digit performance.

It's a KVM hypervisor and I haven't played online, why would they ban you for using a VM?

Re: FreeNAS: Open Source Storage Operating System

#50

Post by josteink »

BrainInAJar wrote: post #47
wilhil wrote: post #43

I have bad memories of freenas (before the split/new version) many years ago when I had a disk and power failure... hdb went, so, c/d moved up a letter and it automatically screwed up raid... ... I was able to recover, but, I remember how many hours I spent on it. Please tell me it is better now?

it's ZFS backed, screwing up the RAID is going to be pretty close to impossible. you can lose the system disk (usb key) that holds your settings, but the data you actually care about will be safe.

> it's ZFS backed, screwing up the RAID is going to be pretty close to impossible

Even if it's ZFS it can get quite messed up if you set it up based on sda, sdb, etc like naming conventions. In that case entire zpools can fail to import in case of failure.

Therefore the best practice is to use device-by-id, so that if a device like sda falls out, the rest of your array should still resolve correctly.

And how the array is created is entirely a FreeNAS thing. Hopefully one which have, like OP says, improved.

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