SOLVED Low-cost SuperMicro Atom C3338 (Denverton) build

[anmnz]

Is in-place similar to this:
?

It is exactly the same thing.

 

[pro lamer]

@anmnz @Arwen thank you for your patient answers :) I've learnt more than expected :) And thanks to the others for (patient?) reading my questions in this thread :)

I would add the replacement disk in as a semi-permanent 3rd mirror.

It seems very nice especially in case of problems with both mirrored disks IMO.

 

[Arwen]

Yes, replace in place is great. Especially for a vDev that has more disks with errors than redundancy, (like both disks of a 2 way mirror having errors). It does requires another disk slot, (though there can be places to work around that issue).

Back in the bad old days, with a RAID set that had more disks with errors than redundancy, many times you were screwed. Some RAID controllers did not support hot-spares, or adding hot-spares after the fact. And even if they did, if you did not have a free slot, it was time for full backup and restore. Plus, the old method of activating a hot-spare was to logically remove the failing disk from the RAID set BEFORE re-syncing the hot-spare. Thus, worthless in the case of more disks with failed blocks than redundancy.

This replace in place also applies to RAID-Z1, Z2 & Z3. For example, if you have 2, 3, or 4 disks failing on Z1, Z2, or Z3, that's too many for pull and replace. Thus, my desire to have a free slot in any ZFS storage server.

As for working around a lack of a free slot for replace in place, if you have a second pool you can export to free up some slots, that's an option. Or even another vDev in the same pool that is healthy. For example, you have a pool of 2 x RAID-Z2 vDevs, one completely healthy, and one with 3 failing disks. Thus, you could off-line a disk from the healthy RAID-Z2 vDev, to free up a slot for your replace in place of the degraded RAID-Z2 vDev.

Last, it should be clear that ZFS will attempt to cause a disk with a block error to spare out that block. So during a ZFS scrub of a pool you can see checksum or read errors, but still have not real problems left afterward. That's one reason why ZFS wants direct access to the disk controller. Any extra levels of indirection, (Virtual Machine or hardware RAID controller), can prevent that from functioning. Only after all the spares are used up, do you get permanent disk block errors. Then it's past time to replace the disk.

 

[Arwen]

Oh, and one trick you can do with ZFS, (and I have done it to grow a single disk pool), is to replace in place a pool with a single disk vDev.

There are lots of reasons to use single disk ZFS pools, (or even non-redundant striped pools);

• Laptops
• Media storage when the originals are available, or backed up
• Backup disks
• Places where you want snapshots but don't need redundancy
  
• Scratch / temporary data, (like decompressed data to be served up and then deleted)
• VM storage, (like on a single SSD), for non-critical functions

I actually use ZFS on non-redundant pools for the first 3.

 

[pro lamer]

As for working around a lack of a free slot for replace in place

Or eSata attached one (providing e.g. an eSATA bracket was prepared before - I guess) if some SATA connectors are available left...

 

[Arwen]

Or eSata attached one (providing e.g. an eSATA bracket was prepared before - I guess) if some SATA connectors are available left...

Oh, stealing my ideas now are we? .

My FreeNAS Mini, (4 slot version), has lots of extra SATA ports, (total of 12, and I am only using 8 internally). So I added a dual eSATA PCIe bracket for 2 of my Intel SATA ports. Then added an external eSATA disk chassis for my backup disk(s). If the FreeNAS Mini XL, (8 slots), had been available, I might have bought that instead. Then reserved at least 1 x 3.5" disk slot for my backup disks.

 

[pro lamer]

Oh, stealing my ideas now are we? :).

Smart brains think alike ;P

Then added an external eSATA disk chassis for my backup disk(s)

So far I am using eSATAp > SATA 22pin 3½" HDD cable and a power adapter for burn-ins.

 

[Arwen]

...
So far I am using eSATAp > SATA 22pin 3½" HDD cable and a power adapter for burn-ins.

Just check hard drive tempeture. I've done something similar, but the hard drive got way too hot. Had to add a fan, also external.

That tempeture issue is why I bought the eSATA chassis I did, it was the only one I could find with a fan.