>>>> ... What if I bought a low-price/low-capacity SSD drive for each >>>> of these systems, installed the system essentials on them, and used my >>>> existing high-capacity HD drives for data storage? Would each system >>>> keep running if the HDs died? If so, I think that would offer as good >>>> or better system reliability than RAID1. What do you think? >>> You don't need to buy SSD "drives" - instead you could use CF cards and a >>> cheap adaptor. These are commensurate in capacity & cost with USB flash >>> drives (4gig, maybe 16gig?), but CF cards "talk EIDE" and you can get cheap >>> pin-convertors allowing you to connect them to EIDE cables and treat them >>> like a hard-drive. >> >> Aren't CF cards much slower than SSD drives and HD drives? >> > > Yep, especially the cheap ones which do not support DMA, just PIO. But > this is not necessarily a problem: After starting all services etc. > there will be very few reads on stuff like /etc and /usr. Just make sure > to put all directories to which you write (parts of /var like /var/log > and the several tmp directories) on an HDD, NFS or tmpfs. Of course, > this all depends on your usage patterns and how much RAM you have. > > If you really need to write to the CFDisk, make sure to buy one with DMA > support (and no, the label "super fast" which is regularly found on > these things does not necessarily mean that it supports DMA). > > One drawback of this configuration: You can never use swap - never! > Neither on the HDD (there is a high chance that the system would crash > when the HDD fails) nor on the (cheap) SSD/flash drive (the drive would > wear down, removing any advantage you tried to gain). > >>> I know of these used in Asterisk based PABX systems & PoS tills with the >>> expectation that they're more reliable than disks, and have read statements >>> by people deploying quantities of such machines that they've never had a >>> failure in years of use. >> >> I like the sound of that. > > Where I work, we have a System-on-a-Chip (SoC) NAS. Albeit being the > second most powerful machine we have in our server room (quad core CPU, > lots of RAM, three redundant power supplies and a good dozen HDDs), the > OSS itself resides on a removable card not bigger than my thumb.
Is cost-savings the advantage of using CF instead of SSD? It sounds like it might be wiser to spend a little more (low capacity SSD drives are pretty cheap now) and have a real storage device that doesn't need an adapter and is much faster, can swap, etc. I bet I'm missing something though...? - Grant >>> I don't know how that really compares to RAID 1 - if you use hardware RAID >>> (and you can get hardware SATA controllers for £50 these days) then you can >>> assign a hot-spare, and hot-swap a replacement drive with zero downtime. >>> With hardware RAID you can still boot if one of the drives fails, but you do >>> add the controller as a potential point-of-failure. >> >> Would the system keeping running if I used a CF or SSD for the system >> install and the HD drive died? >> >> - Grant
