ZFS on version 7.2.6694

[csk]

Hi,
I am new to nas4free and zfs, and after considerable research (over the last one month), I have finally decided to build my has with version 0.7.2.6694 of what used to be called freenas back then.

Reason: I just don't have the budget for latest hardware, and I had an old mobo with 2gb ram in it.

I need your expert opinion on why my build could be called a bad idea, after taking the following into consideration:

1) I have bought a ups, and set it up with the nas (graceful shutdown working fine)
2) I have bought a brand new smps, to protect my hgst drives from power fluctuations.
3) I have 2 x 3TB HDDs, of hgst ( lowest MTBF ), set up in raid 1 (mirroring)
4) my primary use for the nas will be as an archive for family videos and photos.
5) I expect the nas to be used for no longer than 30 minutes on any given day.
6) I liked ZFS primarily because of scrub, will run it once a month.
7) I will be running a CRC check at the stage of dumping data onto the NAS.

Do you find any issues in this build, considering my requirements?

[b0ssman]

that old version is not supported anymore.

try the latest version of nas4free first. you can run zfs with 2gb ram.

[csk]

Thank you for your reply sir, but I read on NAS4FREE site that for ZFS, minimum 4GB RAM is a must.

http://wiki.nas4free.org/doku.php?id=do ... quirements

Freenas requires 8GB. Hence I preferred NAS4FREE, as it seems to be free of bloat.

And since the older versions had even lower RAM requirements, I was thinking of going with them.

Do you have a bad experience with them? For what reason are they not recommended now, besides being not supported anymore?

[Parkcomm]

but I read on NAS4FREE site that for ZFS, minimum 4GB RAM is a must.

ZFS in 2GB is a tight squeeze with any OS. I don't think the latest Nas4Free is significantly bigger than 0.7.2.xxxx and it'd be worth it for the better support for sure. I think you'll find it'll run fine out of the box, but if not there a couple of easy tweaks that'll get you going.

[b0ssman]

armandh is running one of his boxes with 2gb ram.

this is one of the cases where a full install could be helpfull.

[csk]

I was concerned because NAS4FREE itself doesn't recommend less than 4GB.

"I think you'll find it'll run fine out of the box, but if not there a couple of easy tweaks that'll get you going."

What tweaks do you recommend? I only want the scrub feature. Rest I don't mind turning off, as long as I am guaranteed data integrity. Performance is also not a factor for me, as this box would be just an archival box.

Also, I just wanted to understand the following, in connection with ECC memory:

If I am generating my data on a PC w/o ECC memory, and I copy it onto the NAS which has ECC, what use is that ECC from the NAS to me? It wont catch errors committed by the sender PC. And ZFS will anyways help by detecting silent errors while reading from the NAS drives (because I am using RAID 1). And I will be using a program like teracopy, to dump media files onto the NAS, since it has built in CRC checking mechanism. So it seems to me that not having ECC may cause problem during playback of media files, but not in the media files themselves.

Is my understanding reasonably right, or I have a serious conceptual misunderstanding?

[csk]

"armandh is running one of his boxes with 2gb ram."

I found his config:
2 thread 1600 Mhz atom/ion, 1 TB ZFS mirror, available RAM 1.291 Gb, 64 bit NAS4Free-9.1.0.1 rev 573 [27 watts, 35 Mbps]

Would you recommend that I go with NAS4Free-9.1.0.1 rev 573?

[Parkcomm]

ZFS prevents silent bit rot - did you know a gamma ray particle can flip a zero to a one (I shit you not). ECC will pick that if the bit is switched in RAM.

More importantly if your ram goes faulty then ZFS can write bad data to the disk, if you don't have ECC.

The tweaks can be done automatically using viewtopic.php?t=1278 (if required). Or by manually setting in loader.conf.

Code: Select all

# X64_2GB
#vm.kmem_size="1536M"
#vfs.zfs.arc_min="512M
#vfs.zfs.arc_max="512M"

armandh is very active on the forum - why not drop him a PM.

[daoyama]

Thank you for your reply sir, but I read on NAS4FREE site that for ZFS, minimum 4GB RAM is a must.

4GB is not requirement.
NAS4Free requires only 512MB (+swap 512MB) on any platform.
However, ZFS performance is depend on ARC(memory cache), so if you have extra RAM, you can gain some performance.
If you don't mind maximum ZFS performance, you can choose any size of RAM.
In fact, I'm always testing NAS4Free 10.2 on 1024MB and 512MB without any tuning, without any extensions.

If you use NAS4Free latest 9.3 or any of 10.2, you can get more usable memory than any of NASFree 9.2/9.1/9.0, probably any of FreeNAS 0.7.
Recent NAS4Free is using xmd (transparent compression memory disk) for system disk. It saves around 650MB swap usage compare to previous versions.

Important thing is that NAS4Free 10.2 with memory 512MB + swap 512MB is guaranteed upgrading via WebGUI.
(At least, we expect it for FreeBSD 12.x)

[csk]

Thanks guys for all this info. You are very helpful.

@daoyama: thanks for the comforting info. Presently, the NAS is consuming max 35% of the 2GB RAM, so just under 720MB's.

@Parkcomm: I got that concept of bit rot, and why ECC is used. In fact it's used inside HDD's also. I read that apple decided to go with non ECC RAM to lower the cost of their computers, and thereafter everybody followed suit. So mainstream computers don't have ECC RAM, thanks to apple.

But my point is this:
I am not generating any original data on the NAS. All the data which is going to be stored would be generated on non ECC systems, such as my PC and my RaspberryPi. So at that stage, I am completely vulnerable anyways.
Next, while I dump the data onto the NAS, I will employ CRC checks. So even if bad data is generated, atleast it won't be damaged further in the copying process. No data written onto the NAS would be copied without employing CRC.
Thereafter I run a scrub command, ensuring that the data in the mirror is consistent.
So if I am prepared to accept the memory error at the stage of data creation, I don't see how having ECC safeguards my data any more than not having ECC, because there is no occasion for bit rot to affect my data, without it getting detected either by the CRC, or by the scrub.
Atleast that's what it seems to me, based on my understanding of CRC and scrub. But I could be wrong. Please correct me.

In the meantime, I will talk to armandh and see what he has to say. Thanks

[Parkcomm]

I think if you do a CRC to the on disk data you have proven you had no memory corruption for that transaction - will you do this every time you backup you pool, or copy back, or move to new hardware etc? If so I think that is a good solution.

However if you do a scrub and if ZFS reads a block and sees an error because of bad memory it will "correct it". So if you have bad memory, scrubbing is the worst thing you can do.

Which only leaves one other failure mode - your bad memory corrupts your whole pool. (ZFS does not have recovery mechanisms like NTFS, EXT4 etc - it trusts the memory)

Have a look at this - and for further reading there is an interesting PDF embedded in the article http://louwrentius.com/please-use-zfs-w ... emory.html.