SDcard as primary storage?
August 19, 2009 4:55 AM   Subscribe

How reliable would it be to use an SD card as primary storage in a Plug computer?

So, I've been tossing around the idea of getting a Sheeva Plug, to have a low-power-consumption web server, etc.

I am looking into the options for external storage.
Of course a USB hard drive is one possibility, but I don't need all that disk space for it and I would rather not take up all the extra physical space required either.

The Plug has an SDcard slot built into it.
How reliable would it be to use, say, a 16GB SDcard as the primary storage for the device, which is going to be almost constantly reading from it with occasional writing?
Is it just a terrible idea? Or could I get away with it?
posted by jozxyqk to Computers & Internet (3 answers total) 5 users marked this as a favorite
Reliable enough, provided you do all your logging etc to a ramdisk.

I run a few small webservers / firewalls / gateways around the place with 512Mb of RAM and either 512Mb CF cards or small (2~4Gb) SD cards as storage. Most of them boot standard OpenBSD installs off the card. I've modified the startup scripts to mount the cards read-only after boot, copy backups of /var & /tmp to a ramdisk, and mount those directories from the ramdisk. Every few minutes or so a cron job runs to check the ramdisk & flush it to the card if it get over 90% full (this usually only happens every few days); I've also modifed the shutdown scripts to flush them on shutdown. All of them have been running for several years without problem.

In theory, the wear levelling in SD cards probably means you don't need to go to quite so much trouble as I have, but I've just carried my configs over from when I was using CF cards without the wear levelling.

If you plan to run an FTP or HTTP server for uploads, you might want to also load /home into ramdisk, but that'll depend on if the files you upload will fit into the ramdisk. If you need to upload large files occasionally, you can probably get away with putting /var & /tmp on a ramdisk, leaving the SD card mounted read-write, configuring a secondary /temp directory for your ftp/webserver (& CGI / module scripts) on the SD card, and leaving /home on the SD card - all the day-to-day system chugging writes to /var or /tmp, so you shouldn't be hitting the card too often anyway.
posted by Pinback at 5:48 AM on August 19, 2009

Note, I'm not using SheevaPlugs - I'm using fairly standard SBC hardware; microATX and similar. YMMV with the SheevaPlug; looks like you may need to build a custom kernel or modules to boot Linux on it.
posted by Pinback at 5:54 AM on August 19, 2009

This is discussed all the time on PlugForum. Short summary: YMMV. For some people it works great, others, not so good. Brand of SD card seems to matter.

Pinback, the Sheevaplug ships with a stripped-down Ubuntu distro. I'm quite happy with mine. Don't expect to do hefty floating point - it's an ARM. If you need better I/O, there's the OpenRD Client.
posted by scruss at 6:59 AM on August 19, 2009

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