iX FreeNAS Mini XL 2nd SATA DOM?

[ashes00]

Hello all I am setting up my Mini XL, and see that it has QTY (1) 16GB SATA DOM for boot. I have always ran my FreeNAS systems with 2 USB flash drives in a mirror as a safety measure. How can this be accomplished when I'm using a SATA DDOM? Do I need another SATA DOM, or can I use a 16Gb USB flash drive? Thanks in advance.

Ash

 

[Redcoat]

The reliability of the SataDOM is such that most of us using them (or SSD's) for boot will not duplicate/mirror them, finding it unnecessary.

 

[wblock]

Mirroring a SATADOM with a USB drive will reduce reliability, not add it. Just use the SATADOM. Do you back up the FreeNAS configuration regularly to an external location?

 

[ashes00]

Mirroring a SATADOM with a USB drive will reduce reliability, not add it. Just use the SATADOM. Do you back up the FreeNAS configuration regularly to an external location?

Yes I do back the configs up often. Could I do QTY (2) SATADOM in a mirror? The name of the game is N+1

 

[wblock]

Could I do QTY (2) SATADOM in a mirror?

Yes, this can be done. I would personally prefer a single normal SSD over two SATADOMs. The Mini XL has space to mount two 2.5-inch SSDs, assuming you are not using them already for L2ARC or SLOG (unlikely).

 

[ashes00]

Yes, this can be done. I would personally prefer a single normal SSD over two SATADOMs. The Mini XL has space to mount two 2.5-inch SSDs, assuming you are not using them already for L2ARC or SLOG (unlikely).

Just curious why you would prefer a single SSD over 2 diff SATADOMs? My understanding of the SATADOM is it is just a small capacity SSD device. Is not N+1 better than N?

 

[wblock]

SATADOMs are small, special-purpose SSDs. Their whole reason for existence is that they are physically small. They do not have a lot of capacity and generally are not particularly fast. So... if physical size is not a limitation, why not get one of the consumer SSDs with lots more capacity and better speed? I feel that either the SATADOM or a standard SSD are more reliable than USB sticks, and with the configuration backed up, there is usually not a huge need for mirroring SSD devices. If there is a failure, install a new boot device, install FreeNAS to it, and restore the configuration. Obviously there is an inconvenience factor, and a little bit of a time delay. If that's a problem, a mirror can help, although you might have to select a particular boot device on the boot screen after one of them fails.

Come to think of it, SSDs are so cheap now that you can probably set up a mirror of 64G or 128G drives for under $100. That's pretty cheap for the convenience, particularly when people come to use their NAS for so many things.

 

[ashes00]

Yes I would have to play with the boot order some. Okay thanks for your comments wblock

 

[Arwen]

My FreeNAS Mini came with one SATA DOM. Later I added a second as a Mirror. Partly because I wanted the replacement part already bought and available.

 

[Redcoat]

My FreeNAS Mini came with one SATA DOM. Later I added a second as a Mirror. Partly because I wanted the replacement part already bought and available.

Would you choose SATA DOM or SSD "today" (and why)?

 

[Nick2253]

I would always choose an SSD if I had the space and the free SATA port.

I think it might help to understand the vast orders of magnitude difference in reliability between a USB flash drive, a SATA Dom, and a SATA SSD. It's also pretty easy to default our thinking that failures are random events. However, with mirrors, both drives, whatever they are, are subjected to approximately the same wear. This usually means that their failure is highly correlated, not independent. Therefore, having two USB drives doesn't really give you twice the protection. In fact, it may only be slightly better than one USB drive.

When you look at modern SSDs, thanks to their large capacity, high cell longevity, and advanced wearleveling techniques, it becomes highly improbably that you can "wear out" an SSD with the FreeNAS workload in your lifetime. There is always the possibility of an infant failure creating problems, but those are pretty unlikely as well.

In an enterprise environment, where uptime is key, I would always recommend dual SSDs to avoid any downtime issues related to those rare (but possible) infant mortality issues. However, for any typical home user, downtime isn't really a huge problem, and as long as you are backing up your config, you'll be back on your feet as soon as you get another drive. And an SSD will mean, for most, a lifetime of hassle free use, while USB flash drives will inevitably need to be replaced after a couple years, and a SATA Dom within a decade.

 

[Redcoat]

Yes @Nick2253, that's where my head is, too, on the preference for SSD's and single use for boot.

But given @Arwen's so well reasoned and expounded views and history on the Mini (from which I have often directly benefited), I will be interested to see her response and for it to be available for "general consumption". Her earlier post might suggest a preference for the SATA DOM, which surprised me some. Apart from the service/life aspects, for me the $$'s work against them too when compared with SSD's.

 

[Arwen]

My preference for using a SATA DOM as the mirror of my exitsting SATA DOM, is that my 2 x 2.5" disk bays had Mirrored SLOGs in them. Thus, no "normal" disk slot available in my FreeNAS Mini. That worked out so well, I bought another SATA DOM, (and largest available at that time), to mirror my desktop's OS on spinning disk. Which also did not have any free slots.

When I did buy my FreeNAS' SATA DOM, I selected one that was larger, (32GB), than the existing one, (16GB). Turns out to be a good idea. The existing one was a few mega-bytes larger than half the size of my 32GB one. So assuming that new vendor's 16GB was half the size of their 32GB, I'd have had to re-load my FreeNAS OS using the slightly smaller size. As it was, just add it as a Mirror.

Thinking about it today, even if I had free 2.5" disk slots, I would still go for the SATA DOM. Why, you ask? If I had free slots, I might have bought 2 x 1TB or 2TB 2.5" NAS disks and created a second Mirrored pool for general storage. (For my backups, misc. software, all pretty small.) Then used ZFS replication from the small pool to the larger pool. And, then used the 4 x 4TB only for Media files, (and a copy of the smaller pool). Plus, maybe changing the larger pool from RAID-Z2 to RAID-Z1. (I have good backups...)