Advice needed for Atom C3558 build

[pro lamer]

raidz2, mirrors?

When using mirrors you get a bonus backup method... See this thread https://forums.freenas.org/index.php?threads/lower-ram-requirement-for-raid1.68811 and look for split...

Sent from my phone

 

[LimeCrusher]

• Motherboard/CPU: Supermicro A2SDI-4C-HLN4F, Intel Atom C3558
  • Official product page claims it only supports up to DDR4-2133

I like those Atom C boards. A lot of SATA in a small footprint. AsRock has a similar board, I don't know which one is best, they're pretty similar IIRC but you should look around you in terms of price and availability.
I thought about building a NAS with those but I wanted to do some transcoding so I needed a little more muscle CPU-wise. Ultimately, the price and overall product was less competitive than a µ-ATX for my use case but I understand you need to keep a low profile with a Mini-ITX board.

However, I'm a bit nervous about putting that into a Z1 (and I believe others on the forum may caution against it).

I am actually surprised that nobody here vehemently tells you that RaidZ1 is a no-go. The Maths work against you here, let's compute your chance to resilver successfully in the eventuality of a drive failure in a 3 x 8TB RaidZ1 setup:

• You need to read at max 2 x 8TB of data on the remaining drives to rebuild data on the replacement drive,
• Your drives have a URE rate of 10⁻¹⁵ to 10⁻¹⁴.

The chances of successfully resilvering (not getting an URE while resilvering) are:

• about 88% assuming an URE of 10⁻¹⁴,
• about 28% assuming an URE of 10⁻¹⁵.

I don't fully understand the consequences to be fully honest but I am afraid it could range from a corrupt file to the loss of the entire pool. Then, if you have a backup, why not? Would I do it personally if I had a backup? Nah, the numbers freak me out and I wouldn't want have to deal with that.

As you may have read, mirrors have some advantages, flexibility being one of them. Start small with a two-drives mirror vdev at first, buy a couple more later and add another two-drives mirror vdev to your pool. Nevertheless, even if a four-disks RaidZ2 setup may not be optimal, it seems to me that it offers greater data integrity than a pool of four disks in a two mirrored vdevs setup. I am not totally familiar of how resilvering works and how parity is used and the disk loss scenarios is different in the case of RaidZ2 vs mirrors but I tend to think that you're better off with RaidZ2.

 

[Constantin]

It comes down to how much you value you time, data, and how fail-safe the backups are. Nothing wrong with even striping the drives in a NAS as long as you know that the backups are good, the data easily replaced, etc. Conversely, the longer it will take you to come back from a failure, the more you value your time, the more precious the fidelity of the data, the more you should consider Z2 or even Z3 arrays. Not because failure is likely (hard drives for the most part are amazingly reliable) but because the recovery from a drive failure is less likely to lead to pool loss.

Enabling SMART helps, as do scrubs, to help highlight drives before they conk out completely. But as others here have discovered (see this recent thread re: PSU failure leading to pool loss), pools may get killed by random events no matter what you do. Every step towards making the pool more resilient will improve your odds (mirrored SLOGs, mirrored boot devices, dual-redundant power supply (PS), dedicated uninterruptible power supply for each PS, etc.) but ultimately there are parts that cannot be easily made redundant in a home setting, such as the motherboard itself.

There are plenty of great resources out there dedicated to explaining the benefits and drawbacks to various pool configurations. Learn then settle on a pool layout that allows your pool to function for you. Don't be afraid either to re-configure stuff later on. If the backups are good (and I'd suggest having multiple sets), then there is minimal risk in nuking and rebuilding pools from the ground up. I did this with my latest pool, enabling the use of a mirrored SLOG by eliminating one of the spinning hard drives.

I'd have a look at this board also as an alternative to the C3xxx series: The Supermicro X10SDV-2C-7TP4F. It features two PCIe 3.0 x8 expansion ports, two gigabit ports, a IPMI management port, two 10GBe SFP+ ports, a on-board LSI 16-Channel SAS controller, a PCI 3.0 x4 port for m.2, a 2-core/4-thread Xeon D 1508 (25W TDP), two SATADOM connectors, etc. and all that in a flex ATX board for about $500. Check the thing out, it's a pretty amazing solution for a SOHO build where you don't have to support a lot of users at once.

IMO this board is a better value than the C3xxx series because you get the benefit of a fairly future-proof assembly for the same or less money than the C3xxx offerings out there. There are more powerful Xeon-D versions out there that will need more Watts and which will also cost more. But the price overlap between the Xeon D series and the C3xxx series is somewhat baffling. As best as I can tell, the main benefit speaking in favor of C3xxx is lower idle power consumption.