Does a USB flash drive make a viable long-term system disk?

[Barnaby W. Füi]

Say I were making a small Linux NAS machine. Instead of using up a SATA port and cluttering the storage drives with some extra small partition to run the OS off of, it seems to make perfect sense to use a small SSD. However, SSDs, even on the low (and thus crappy) end, are at least $50-ish.

But a Flash drive would seem to solve all of those problems: I could connect it internally to one of the abundant USB headers on the motherboard (and who needs tons of USB ports on a NAS system anyway?); and I can find a high quality, decently performing flash drive with tons of reviews for about half the price of the lowest-end SSD.

So that leaves two questions:

1. Is the performance really good enough (random I/O, and writes)? It doesn't need to be fast. Just not terrible. Flash drive performance is usually only considered in the context of copying files to/from them. Running a live OS is probably going to stress random I/O more.

2. And speaking of writes... durability is the other question. I would rather not disable all logging (logs can be indispensable if something goes wrong), so there will be a slow but steady trickle of writes to the drive. Is it going to randomly corrupt a year or two down the line?

 

[Barnaby W. Füi]

I guess I could have done a bit more homework. This review of a Patriot Xporter shows pretty respectable speeds, with only random writes being particularly slow. And they even mention that modern flash drives have wear-leveling, which I wasn't really aware of. So it sounds like this plan would work out fine.

Although if anyone has any real-world anecdotes, I would still love to hear them.

 

[Blain]

I've got an Xporter and love it. It's very fast and easy to use.
Out of the USB drives I've used, my favorites are the Patriot Xporter and the Corsair Voyager.

 

[sub.mesa]

USB flash uses 3-bit MLC and has only basic wear leveling; running an OS on such a device could make it fail within a few months due to write amplification and lack of proper wear leveling.

That's the main difference between USB flash and SSDs; the latter have advanced controllers and use only 2-bit MLC to get write amplification under control when doing random writes.

USB sticks usually are very slow on random writes, and do not support write remapping. Thus, they should only be used to store large files (sequential I/O).

 

[Rifter]

Not a good idea, will wear out real fast.

 

[frostedflakes]

Yeah, an SSD isn't that much more expensive per GB, and will be much faster and more reliable. The only OS that would run well off a USB flash drive is something like Puppy Linux, which loads itself into RAM.

 

[Barnaby W. Füi]

Interesting. And bummer!

 

[ElFenix]

how many writes could a linux nas machine really be using? plenty of people use compact flash cards in a simple IDE -> CF adapter for that sort of thing. depending on what distro you're using everything can be done in memory (any live CD bootable distro works this way)

 

[Mark R]

FWIW I got a 1GB USB as a free gift from some show or other about a year-18 months ago. Hopelessly slow, the worst I'd ever used (about 1MB/s writes).

Anyway, I set it up on a NAS box to operate as a cache for downloads, web, logs, blah. After about a year, it had had about 4 TB of writes and was still going strong.

 

[corkyg]

I see no particular advantage to using a flash drive for the OS. Unless you have a new system with USB3, it will be strangled by USB2. I use one, but for emergencies only and laptop clonings.

 

[taltamir]

USB flash uses 3-bit MLC and has only basic wear leveling

USB flash WILL use 3-bit MLC... AFAIK intel just started producing 3-bit MLC, all the USB flash on the market still uses 2-bit MLC.

I see no particular advantage to using a flash drive for the OS. Unless you have a new system with USB3, it will be strangled by USB2. I use one, but for emergencies only and laptop clonings.

1. save money (if you don't have a crappy old drive lying somewhere, I am using a 160GB PATA drive for my fileserver's OS)
2. save space (USB stick is tiny!)
3. save power.

Not a good idea, will wear out real fast.

its a fileserver OS, what kind of writes will it be making to the flash drive that will wear it out?

 

[taltamir]

delete

 

[frostedflakes]

USB flash WILL use 3-bit MLC... AFAIK intel just started producing 3-bit MLC, all the USB flash on the market still uses 2-bit MLC.



1. save money (if you don't have a crappy old drive lying somewhere, I am using a 160GB PATA drive for my fileserver's OS)
2. save space (USB stick is tiny!)
3. save power.



its a fileserver OS, what kind of writes will it be making to the flash drive that will wear it out?

Actually I guess I missed the part where OP said it was a file server OS. A lot of those are actually designed to run on CF cards or other flash media, so running one on a USB flash drive should be fine.

 

[BTA]

When I was running a FreeNAS box I used an old USB stick to run the OS off of. Worked fine for quite a while.

 

[Barnaby W. Füi]

how many writes could a linux nas machine really be using? plenty of people use compact flash cards in a simple IDE -> CF adapter for that sort of thing. depending on what distro you're using everything can be done in memory (any live CD bootable distro works this way)

The only writes it'll probably be doing are logs.

Looking in /var/log on my desktop machine, I see about 50 lines written per hour, spread across three files, when the machine is idle. Most of that is dhclient because apparently our dhcp server has a really short lease time.

On the other hand, the NAS might run some services that log more frequently.

After thinking more about it, it wouldn't be that annoying to use the data drives for the OS also. I could just set aside a few gigs on each drive and RAID 1 or 5 them together. It would be more reliable and also require less hardware.

 

[jjmIII]

Anyway, I set it up on a NAS box to operate as a cache for downloads, web, logs, blah. After about a year, it had had about 4 TB of writes and was still going strong.

I'd love more info on setting that up!

 

[Yellowbeard]

When I was running a FreeNAS box I used an old USB stick to run the OS off of. Worked fine for quite a while.

I have been running a FreeNAS server from a 1GB flash drive for about 3 years now. I don't think you need to worry with short term failure using a small Linux kernel any more or less than you would with a standard HD.

Also, when using FreeNAS, you cannot use the OS drive for data. I do not know if this limit applies to other OSs of this type.

 

[Barnaby W. Füi]

Also, when using FreeNAS, you cannot use the OS drive for data. I do not know if this limit applies to other OSs of this type.

I was planning on using mdadm + lvm with Linux. This basically allows you to set up any conceivable combination of partitions/raid you want. I would probably reserve a few gigs on each physical drive, and then raid those small partitions together to be the OS partition. The remaining space on all the drives would be raided together to store the data.

But it wouldn't have the GUI of FreeNAS.

 

[Yellowbeard]

I see no particular advantage to using a flash drive for the OS. Unless you have a new system with USB3, it will be strangled by USB2. I use one, but for emergencies only and laptop clonings.

In the specific instance of FreeNAS, you can't use the OS drive for data. So, using any HD would be a complete waste of potential storage space. That's why a small flash drive was perfect IMO. You could even do it off of a CF card.

 

[pjkenned]

FreeNAS runs well on a USB drive because it does not do much writing to the disk. From what I have seen it runs from RAM and mostly just writes to save configuration type items to the USB drive. Writes occur on the system disk much less than on the average Win7 system.

 

[Modelworks]

Get a compact flash card with an adapter. There are a ton of routers out there using CF for the OS storage. I use a 4GB card in a IDE adapter.
http://www.newegg.com/Product/Produc...-002-_-Product

It also has the advantage of appearing like a HDD to most OS.