Has anyone tried throwing 3~4 2GB CF II Cards thru IDE adapters in a striped RAID array? Should be interesting to see the performance, sustained transfer speed would be comparable to a regular HDD but what about access speeds? Wouldn't reading from Flah Memory have much lower latency than a mechanical hdd?
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CF II Cards in Striped RAID???
- Thread starter statik213
- Start date
... and still be half as fast as a decent single HDD? Besides, CF is PATA, with the drives supporting MWDMA2 mode at best and having zero (yes zero) cache. Since PATA does not do concurrent access, you don't get 20 MB/s from two 10 MB/s drives on the same IDE channel, you get 10.
uOpt
Golden Member
Just for the kicks I built a RAID-5 on three raw device which were on:
- a CF card on my mp3 player
- a file on a network-mounted filesystem
- a file on a memory filesystem
It was only done as a pissing contest to show people what software RAID can do, as opposed to hardware raid or raid provided only for specific controllers. As in "if one of your RAID-5 slices goes down, you can use any space you can scramble together, anything, anywhere, to hook it back into your RAID-5".
At the time Linux did not have a network filesystem interface to gmail, that would have been the final hack 😀
- a CF card on my mp3 player
- a file on a network-mounted filesystem
- a file on a memory filesystem
It was only done as a pissing contest to show people what software RAID can do, as opposed to hardware raid or raid provided only for specific controllers. As in "if one of your RAID-5 slices goes down, you can use any space you can scramble together, anything, anywhere, to hook it back into your RAID-5".
At the time Linux did not have a network filesystem interface to gmail, that would have been the final hack 😀
What use is almost-zero access time when you don't get good throughput afterwards? The couple of milliseconds saved on the headstart will very soon be used up by the much much slower data transfer. Besides, write latency isn't even that good because a flash "sector" must first be erased before it can be written to.
Swap file on a FlashROM drive is particularly brilliant (NOT) because FlashROM cells have a limited number of erase/write cycles before they die. With the typical lifespan being 100,000 cycles, the heavy read/write activity on a swapfile will kill them within days.
If you want real zippy storage, you can use Quantum's RAMdrive devices - these are RAM arrays on a SCSI interface, with a real HDD as a nonvolatile backup. On recurring reads as well as writes, these have zero access latency and around 300 MB/s throughput. And if you want your machine to be faster although it's using the swapfile, then don't make the swapfile faster, add more RAM.
Matthias99
Diamond Member
I did just want to note that some applications are almost ENTIRELY access-time limited (for instance, databases with a large number of very, very small records). If you're reading and writing 1K blocks of data all day, and all you care about is doing the maximum number of those operations per second, this would be WAY faster than a RAID of regular hard drives, because the hard drives will spend 90+% of their time seeking. Even desktop use tends to be dominated by seek/response time; how often are you loading 50+MB files (unless you're doing video/photo editing)?
A hard drive RAID might be a good order of magnitude (~100MBps versus ~10MBps) faster than straight flash-based storage. But access time for the flash storage will be *several* orders of magnitude better than on a hard drive (maybe .1ms or lower versus ~10ms).
Of course, you can't use standard flash memory as a swapfile, because (as noted) you'll kill it fairly quickly. You could, however, install programs on it, or use it to store frequently-accessed-but-infrequently-updated data. Flash-based drives that don't quickly die are available, but cost a ton. RAMDisks (with or without disk backup; you can get ones that just have battery backup as well) are MUCH cheaper (relatively speaking), and also have next to no latency and very high throughput.
Matthias99
Diamond Member
You might try a Google for "PuRAM" or "SSD" or "Solid State Disk". That should turn up a lot of info.
It might be an ok idea for a solid state silent computer that maybe just boots a small linux off the CF and runs in a RAM disk the rest of the time. You could do it even cheaper with something like knoppix on a CD, but then you have some moving parts. Coupled with a passively cooled cpu, that could be a nice system for basic internet use or for file serving if you don't mind adding some big IDE drives.
Physically, the number of write/erase cycles is much less than 100k on modern flash cards. It's actually more in the range of 10k (for MLC, binary is a bit better). Steps are taken logically, however, to improve the lifetime of the card through wearleveling and other block managment techniques.
The transfer speed is being improved though. In the coming year, don't be surprised to see 66MB/s data transfer rates.
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