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On Thu, 29 Apr 2010, Grant Sewell wrote:
On Wed, 28 Apr 2010 23:28:19 +0100 Julian Hall wrote:Something I've wondered about for a while, but keep forgetting to ask. As I understand it, SSD lifespan is measured in numbers of r/w cycles, as discussed at http://hothardware.com/News/Two-Methods-for-Measuring-SSD-Lifespans/ With that in mind is it such a great idea to put an OS on an SSD as it will be almost constantly engaged in readign and writing, far more so I would have thought than a data drive - depending on the user of course. JulianIs it such a great idea to put an OS on an SSD? If the lifespan is rated in the number of write actions on any given part of the drive, then it probably wouldn't be a very clever idea putting the regularly changing parts of the system on it... /var, /home? But the bits that don't change very often... why not? The beauty is being able to have all the various bits of the filesystem spread out in multiple places and yet still have it work nice and cleanly 'cos you've mounted them in the right place.
My thoughts (based on my own experiences and what I've read) are that with modern hardware it's not going to be an issue. Well, maybe 5+ years down the line, but you'll probably have something new by then...
My little embedded PBXs started life with a 48MB IDE disk module (plugs directly into an IDE socket), and a separate 48MB module for voicemail storage. My bootstrat creates a 128MB RAMdisk and unpacks everything into the RAM disk and runs from there. Config data is written back for the first IDE drive to a separate partition. (And I use direct writes - it's not a filesystem!) The 2nd drive is formatted ext3 with noatime and long write butter files to minimise writes to it.
These days I just put in a single 256MB module, or in the newer ones a 256MB Compact Flash device. I still run everything from RAM - makes it as fast as a fast thing - good on a slow processor, although I've relented and keep voice promots on the flash device now - which Linux kindly caches in RAM for me the first time they're read.
I tried to build my AAO that way, but it only has 512MB of RAM, and by the time I'd built the image, it struggled to run from a 300MB RAMdisk which left next to nothing for the aplications to use. Maybe that extra 1GB of RAM is looking worthwhile now...
But if you want the ultimate in performance, get loads of RAM and stuff root, /usr, /var, etc. into a RAMdisk and off you go. (just remember to write any changes back somewhere non-volatile every now & then ;-)
Gordon -- The Mailing List for the Devon & Cornwall LUG http://mailman.dclug.org.uk/listinfo/list FAQ: http://www.dcglug.org.uk/linux_adm/list-faq.html