On Fri, Jul 11, 2014 at 06:52:07PM -0700, ToddAndMargo wrote: > On 07/11/2014 06:12 PM, Konstantin Olchanski wrote: > >On Fri, Jul 11, 2014 at 04:02:09PM -0400, Andrew Z wrote: > >>> > >>>... synchronizing a flashing drive (target) with my hard drive (source) ... > >>> > >>>Problem: it is slow -- takes three hours. To help the > >>>speed issue, I upgraded from USB 2 to USB 3. Backup went > >>>from 3 hr-15 min to 3 hr-5 min. It is almost faster > >>>to wipe the stick and rewrite it. > >>> > > > > > >The main question is this: what is the actual write speed of your USB flash > >media? How about the re-write speed? > (not the same, obviously - as it requires as erase step). > > Kanguru SS3: Read 105 MB/sec; 78 MB/sec >
Right, this is almost SSD quality flash, but for some reason, performance for writing small files is much worse compared to SSDs. One would think that one could make a USB flash disk with same performance as SATA flash (SSD), but perhaps nobody makes the right flash controller chip and a dual chip solution is not workable (an SSD flash controller behind a USB-to-SATA interface). More likely, though, is that the USB form factor, power budget and cooling capacity does not permit implentation of full-performance flash disks. One would think that USB3 can provide enough juice, but maybe there are still problems with cooling and maybe they do not want to make a device that would not work in a USB2 slot... K.O. > > Don't have the re-write speed. > > > > >I ask because I use USB flash media as boot and linux system disks on > >embedded machines (VME SBCs) > >and I have looked at different USB flash media. Most of them are very slow, > >actually it is very hard > >to find "fast" USB flash media. > > The cheap ones crawl. If you spend a little: > > El-Cheap-O: > Read: 3 MB/sec > Write: 2 MB/sec > > Kanguru SS3: > Read: 105 MB/sec > Write: 78 MB/sec > > Kanguru Flash Blu 30: > Read: 145 MB/sec > Write: 8GB: 25 MB/sec > 16,32,64GB: 45 MB/sec > > Kingston Data Travler: > Read: 70 MB/sec > Write: 30 MB/sec > > Kingston Data Travler Hyper-X 3.0: > Read: 225 MB/sec > Write: 135 MB/sec > > For comparison: IntelSSD 530 Series SATA 3 flash drives: > Sequential Read: 540 MB/s > Sequential Write: 490 MB/s > > >The common media you get for $10 at Staples is "read 30M/s, write 10M/s" > >(regardless of USB2 or USB3 interface). > > Worse than that! > > > This is probably consistent with the speeds that you see. > > > I went from 20 MB/sec to 78 MB/sec. Took 10 minutes off of > three hours. > > > > >With some work, you can find media that writes at 20-30M/s, as measured by > >timing "dd", but drops > >severely when you time "rsync" (must be inefficient at writing small files). > > > >So when you select a brand USB flash drive for your workload, as you run > >"rsync", watch > >the output of "vmstat 1" (the "bo" column is Mbytes/sec written to disk) and > >the output of "iostat -x 1" - you will see %util pegged at 100% and "svctm" > >(in msec) running > >in 1-10-20 seconds for "slow media", a little bit smaller for betyter media. > >For HDDs and SSDs, > >the "svctm" is in low milliseconds. "svctm" is the request service time - > >time from sending > >a request to the drive and getting the reply from the drive that the request > >is finished. > > > >Some USB drives advertize high write speeds (not "up to" but actual "will > >write at" promises), > >you can try those ($$$), but you will probably find that the speed of > >"rsync" does not reach > >the promised rates because of inefficiency of flashing small files. > > sda is the source hard drive; sdc is the target flash drive > > $ iostat -x 1 > > Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s > avgrq-sz avgqu-sz await svctm %util > > sda 0.00 0.00 28.00 0.00 7168.00 0.00 > 256.00 0.08 2.79 1.39 3.90 > > sdc 0.00 0.00 0.00 280.00 0.00 7406.00 > 26.45 1.34 4.74 3.25 90.90 > > > Couldn't find "svctm". > > Does the above tell you anything? > > > > > >P.S. Another problem with USB flash drives - all brands except for 1 or 2 do > >not survive > >being used as linux system disks - they brick themselves within days or > >weeks. I notice > >that they tend to run quite hot, so I suspect they simply overheat and die. > >Actually, > >I did not find a single USB3 flash drive that survives use as linux system > >disk yet. > >By luck I have enough Patriot RageXT 8GB and 16GB USB2 flash media, these > >seem to last. > > There is a lot of trash out there. I refuse to sell Buffalo, > as have had almost 100% returns on them. > > > -- > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > Computers are like air conditioners. > They malfunction when you open windows > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- Konstantin Olchanski Data Acquisition Systems: The Bytes Must Flow! Email: olchansk-at-triumf-dot-ca Snail mail: 4004 Wesbrook Mall, TRIUMF, Vancouver, B.C., V6T 2A3, Canada
