ssd/flash-based drive for an energy efficient home server?

rwd · 2009-10-04 15:01:20

I've built a small fanless atom based home-server for a webserver/nas/streaming audio tasks. I've put two harddisks in it for data. But I wonder if there would be any advantages to running the OS on a additional solid state disk, be it SSD or DiskOnModule? I imagine I can let the harddisks spin down so it would be more silent and energy efficient.

Last edited by rwd (2009-10-04 17:33:49)

intgr · 2009-10-04 16:46:00

A real SSD (solid state disk) is probably an overkill for this task and they can cost many times as much as a flash card of the same size.
If your motherboard still has an IDE port then CompactFlash is a good idea, because they always contain an embedded IDE controller (you need a simple adapter). If not, SD (secure digital) cards with a USB adapter are usually the cheapest.

The caveat however is that flash cards do *NOT* have hardware wear levelling. Each flash block typically has 100 thousand write cycles and isn't guaranteed to last beyond that. Running a typical file system like ext3 can easily create write "hotspots" in the journal area and result in bad blocks.

The usual advice is to use ext2 instead, as it does not have a journal. Using the "noatime" mount option also reduces file system writes. However, with ext2 you can lose data if your system happens to crash at a bad moment. And you still have to worry about write hotspots.

Another alternative is trying out the experimental 'btrfs' copy-on-write file system. Disclaimer: This is experimental software. I have not verified whether btrfs's writes may cause hotspots. But its design is more suited for flash storage in general.

rwd · 2009-10-04 17:29:55

btrfs looks interesting but I haven't found any info about it's wear-leveling capabilities either. Searching for filesystems and flash I also came across UBIFS by Nokia which seems to be a filesystem for raw flash access, even though there aren't any tools in for it in Aur.

intgr · 2009-10-04 17:41:44

btrfs does not do wear-levelling in the usual sense of the word, but its copy-on-write semantics mean it's better suited than older disk file systems.

As far as I know, file systems like UBIFS and JFFS2 only work on special MTDs ("memory technology devices") which provide a raw flash interface to the kernel. These are only available in specialized embedded devices. Normal flash cards are not compatible.

gradgrind · 2009-10-04 18:28:35

If you want it as a home-server you probably won't need to write to it, so you could also consider a read-only system - that will by definition not have this problem. Probably the easiest way to do that is by using aufs, with the top, writeable layer in tmpfs, such as most live systems do. I have a media player on compact flash which has been running for years (I just put a larch live system on it together with grub - using the session saving feature it is even possible to do modifications without too much effort).

rwd · 2009-10-04 19:10:42

gradgrind wrote:

If you want it as a home-server you probably won't need to write to it, so you could also consider a read-only system - that will by definition not have this problem. Probably the easiest way to do that is by using aufs, with the top, writeable layer in tmpfs, such as most live systems do. I have a media player on compact flash which has been running for years (I just put a larch live system on it together with grub - using the session saving feature it is even possible to do modifications without too much effort).

That would solve the wear problem for sure. However if I would run the system in memory ( tmpfs) I could just as well load it from the harddisk instead of a flash drive.

Last edited by rwd (2009-10-04 19:24:06)

gradgrind · 2009-10-05 13:11:58

That's true, it rather depends on how much memory you have and how much you are willing to sacrifice to the operating system. An extra bit of RAM would probably be quite a bit cheaper and simpler than a flash device.

Last edited by gradgrind (2009-10-05 13:12:21)

intgr · 2009-10-05 13:58:27

gradgrind wrote:

An extra bit of RAM would probably be quite a bit cheaper and simpler than a flash device.

Not true, you can buy 8GB flash cards for $20 these days.

Arch Linux

#1 2009-10-04 15:01:20

ssd/flash-based drive for an energy efficient home server?

#2 2009-10-04 16:46:00

Re: ssd/flash-based drive for an energy efficient home server?

#3 2009-10-04 17:29:55

Re: ssd/flash-based drive for an energy efficient home server?

#4 2009-10-04 17:41:44

Re: ssd/flash-based drive for an energy efficient home server?

#5 2009-10-04 18:28:35

Re: ssd/flash-based drive for an energy efficient home server?

#6 2009-10-04 19:10:42

Re: ssd/flash-based drive for an energy efficient home server?

#7 2009-10-05 13:11:58

Re: ssd/flash-based drive for an energy efficient home server?

#8 2009-10-05 13:58:27

Re: ssd/flash-based drive for an energy efficient home server?

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