Slow SSD

[azurianarcher]

Hey everyone,

I'm running fedora core 15 and I'm experiencing a weird problem. My guess is that its something to do with my SSD. My current setup has a raid-0 array for data and an ssd for the root. Whenever I transfer files from the raid array to the ssd, the transfer starts off at around 200MB/s, but quickly drops off. It usually ends up leveling between 70-90MB/s. Is this normal behavior or do I have something set up wrong?
The ssd is formatted with ext4 and has the discard option set. I also have run fstrim on the root filesystem.
The raid array is also formatted with ext4, mounted with the default options
if anyone needs more information about my setup i'll be happy to provide it

thanks,
Max

[Mudgen]

What speeds do you see if you dd a file from the raid to /dev/null? I'm guessing that the 70-90 you see is the raw read speed from the raid, and the transfer to SSD starts out higher due to buffering.

[azurianarcher]

What speeds do you see if you dd a file from the raid to /dev/null? I'm guessing that the 70-90 you see is the raw read speed from the raid, and the transfer to SSD starts out higher due to buffering.

Now that's interesting and it would make perfect sense. I ran the dd test from the ssd and the raid array using the same 8.5gb hd movie. The raid array scored 306MB/s and the ssd scored 501MB/s, which is pretty damn fast for both.

One thing I did see, however, is that transferring that 8.5gb movie to the sdd was again slow, starting at around 200MB/s and bottoming out at 91MB/s. It seemed to stutter at some points, the whole transfer would stop for a few seconds and then start up again. Transferring back (from the solid state to the raid array) scored 480MB/s, what? im not sure what to make of such a high number.

[Mudgen]

Shoots down my guess, for sure. The speed of SSD to RAID is also definitely a quandary, given everything else you state.

I'm running F15 on this laptop, but not a fan. Have left everything else in the house on F14. Wonder what the results would be with F14, live or rescue? Can't point to anything, just sayin'.

[azurianarcher]

Shoots down my guess, for sure. The speed of SSD to RAID is also definitely a quandary, given everything else you state.

I'm running F15 on this laptop, but not a fan. Have left everything else in the house on F14. Wonder what the results would be with F14, live or rescue? Can't point to anything, just sayin'.

I think the results must be the result of caching. I rebooted and ran the ssd to raise test twice in succession. The first time transferred at just over 200 MB/s with some significantly slower parts (it hit 23MB/s at one point). The second transfer varied between 310 and 200 MB/s, odd results. Has that much really changed from f14 to f15 besides gnome 3?

[Mudgen]

I think the results must be the result of caching. I rebooted and ran the ssd to raise test twice in succession. The first time transferred at just over 200 MB/s with some significantly slower parts (it hit 23MB/s at one point). The second transfer varied between 310 and 200 MB/s, odd results. Has that much really changed from f14 to f15 besides gnome 3?

Yes, the initial higher speed smells strongly of cache buffering. What's strange is the drop to 70-90Mb/s afterward. That's about what I see raw on single-disk SATA2 systems.

Like I said, I can't point to anything in F15 to account for it; the biggest under-hood change is probably from sysvinit to systemd, which should have no bearing on io speeds.

[phillip52]

New SSD isn't likely to continue performing at the same level it did when you first pulled it out of the box. That's important to know, given the speed with which SSDs have proliferated in the marketplace amid claims that they're faster, use less power and can be more reliable, especially in laptops.