Drive bays supported meaning and USB drive enclosures

[Realistic]

Hi,
I am looking at upgrading my storage via external USB HDD enclosures. Specifically getting a total of 8 disks in 2 4 disk enclosures. I currently have 3* Toshiba N300 6TB and 3* Toshiba N300 10TB. Both drives have specified on official website Drive bays supported 1-8. Does this number mean that the maximum number of drives per drive enclosure is 8, or maximum number of drives in drive pool or something else? Also are the USB attached drives going to work just as normal drives or could there be some problems. Any answers would be appreciated.

 

[Arwen]

In general, we, (here on the FreeNAS forums), do not recommend USB attached disks for continuous storage usage. The USB connector is generally not as reliable as external SAS connections. Nor is the protocol as robust for storage, like SAS or SATA. Further, many USB to SATA interposer boards do not pass through all the disk related commands, like SMART. Last, some USB storage devices also support primative RAID, which is not recommended with ZFS.

Sorry, here in the FreeNAS forums we tend to be cautious, conservative and careful with our storage. Less problems that way.
USB attached disks add just another layer of complexity that people looking for reliable, long term storage just don't need.

That said, using USB for backup drives or transfer drives do work reasonably well.

 

[blueether]

USB for storage seems very much frowned on here - too many points of failure, dodgy chip-sets...

 

[Realistic]

I see your points, but I have to give some counter points here. Regarding reliability I am already only using consumer grade hardware, non ECC RAM so I really don't think I am downgrading much here. I have my data backed up on external drives so a failure of the system would not be the end of the world. Also even if the system would fail the likely hood of enough drives failing to lose the pool is really low.
The problem I acknowledge from your post is the unreliability of the USB protocol with possible dropping connections etc. That is indeed a problem, but again I have been using USB drives for backups for a while now and haven't had these problems. SMART with USB drives indeed does not seem to be an option which does suck but it is not the end of the world. Regarding the primitive RAID I have read the Freenas manual and know that it is not supported, so I plan on getting a device with JBOD configuration.
The device I was looking at also has a fan for keeping disks cooled (USB enclosure).
Really the only other option I see without going to SAS and much more expensive hardware is SATA multiplier or SATA cards. SATA cards usually have maximum storage capacity specified too low. And SATA multipliers seem like even a greater risk as they might not work at all. Does anyone have any experience with either of those?
I would still like to know what Drive bays supported 1-8 actually means.

 

[Linkman]

The 1-8 drive bays is for number of drives in a single enclosure, most consider it more marketing than anything else. Nothing to do with the number of drives in a vdev or pool.

 

[Realistic]

Thank you for the answer Linkman.

 

[Arwen]

@Realistic, That does look like a nice USB enclosure.

One of the problems with USB enclosures, is if it drops offline. That would take 4 disks out of service. Unless you mirrored 4 to 4, your pool becomes un-available until you fix the issue. Even if it were only a few seconds of drop, that may be long enough to cause ZFS to consider the disks offline.

Most of the time that should not damage the pool. Simply fix the USB problem, (if it did not come back by it's self), and on-line the pool / disks.

However, there are issues with drive writing caching. ZFS counts on drives not lying when data is written to disk. But a USB enclosure may lie and say data is written before it's actually written to disk. That's when ZFS can't compensate. Of course, it's only a problem if you have that type of lying controller chip AND you have the disk enclosure drop offline during a write. So, you should probably run a scrub ANYTIME your USB enclosure drops offline, (if it ever does).

Anyway, good luck.

 

[Realistic]

@Arwen Thank you for a very comprehensive answer.