R/W Times of Running SDHC and Pen Driveas as well as durability
 

O.K. First off, this is a continuation of this thread. I am sorry I started a new one but I wanted the discussion to head in a different direction. The other thread was http://www.linuxquestions.org/questi...48#post5407048

My firsy question, well I wont ask it Ill do reasearch. I just always seem to remember doing doing -xcvf to untar files but most people run tar -xvf .... Sure the man and help files will help me out there so no worries.

On to the main subject.

I made, what I now see was obviously an idiotic post in the other thread. What I am surprised I was not corrected on even as a newbie. I stated as long a pen drive writes 300 MB/S I am O.K.

Well I did some research tonight and apparently it does now. Well let me rephrase that, some do - as per, http://usbflashspeed.com/

Anyways I ran the fowolling commands on an OLD pc running Kali just os USB, HD ripped out. Fan slightly verheatinf, yadda yadda yadda. Still deciding whether it is worth saving, if it is Fan has to be fixed first LOL. Anyways. Here are some results I go .... on recommended linux command benchmarks



root@kali:~# dd if=/dev/zero of=speetest bs=1M count=100
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 0.1292 s, 812 MB/s
root@kali:~#


(OK So, Slightly Confused Here, It is 3X the 300 MB/s I thought wuld be ok t run an OS on)




root@kali:~# dd if=/dev/zero of=speetest bs=1M count=100 conv=fdatasync
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 0.126067 s, 832 MB/s
root@kali:~#


(Again, same results - and honestly on Kali Im not sure if this is USB2 or USB3 but I have to assume 3 at the moment)




root@kali:~# dd if=/dev/zero of=speedtest bs=64k count=3200 conv=fdatasync
3200+0 records in
3200+0 records out
209715200 bytes (210 MB) copied, 0.203332 s, 1.0 GB/s
root@kali:~#


(OF Confused Again But thinking "Cool" at this point, right ? )




root@kali:~# dd if=/dev/zero of=speetest bs=1M count=100 conv=fdatasync
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 0.129324 s, 811 MB/s
root@kali:~#


(OK More Of The Same, Looking Good!)




root@kali:~# dd if=/dev/zero of=speedtest bs=64k count=3200 conv=fdatasync
3200+0 records in
3200+0 records out
209715200 bytes (210 MB) copied, 0.199759 s, 1.0 GB/s
root@kali:~#


(Again looking good)




root@kali:~# dd if=speedtest of=/dev/null bs=64k count=24000
3200+0 records in
3200+0 records out
209715200 bytes (210 MB) copied, 0.101157 s, 2.1 GB/s
root@kali:~#


(Wow, well speed doubled, ain't I special? This seems way to high for a USB stick even though I ahvent messed with them for years though.)





Hmmmmmm
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root@kali:~# hdparm -tT /dev/sda1

/dev/sda1:
Timing cached reads: 2676 MB in 2.00 seconds = 1338.12 MB/sec
Timing buffered disk reads: 56 MB in 3.05 seconds = 18.38 MB/sec



(THIS is where I get confused, and I know, I should understand. I get buffered is essentially what the RAM is holding on to before the HD writes it. Or before the memory writes is. I COULD BE WRONG here, just my comp 101 from a decade ago kicking in. This speeds sam faster than I EVER THOUGHT THEY WOULD as RAM is not known for its exceptional speed unless yu get into graphics card memory or high end build into multi core Processor
Memories- sorry if Im blanning Im tires.

I am lost on what timing buffered disk reads mean ? As well as why it is so DAMN slow ??


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Bonnie I did not Install - I had some errors but will try later
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But honestly what is the best flat out benchmark test for Unix R/W times ?

What is acceptable to run OS off Pen Drive or SDHC ?


Sure I'll ask more as answeres persue but this is a very LONG start.

Thank You to all of you who are considerate and really try to help - even if I didn't help myself QUITE as much as I could have here :(

In a nutshell, usb1.1 is the slowest that I would recommend, preferably usb2.
I have run, & still do, different Linux distros & BSD from both pendrives & SD cards without any problems.
:)

Few things

1) Your dd dumps are not NEARLY big enough. You're just talking to the cache, you're not actually testing the drive speed. You should be dumping in at least double your RAM's capacity if you want a good test. Yes, that usually means dd dumps of 10+ GB.

2) USB 3.0 ports are generally either blue or they say "SS" on them (super speed). If it's not blue and doesn't say SS, then it's a USB 2.0 port and is limited to a max of 40 MB/s, realistically more like 25-30 MB/s. USB 1.1 is from the 90s, I'd be surprised if any machine with USB 1.1 ports is still operational.

3) RAM is incredibly fast, modern machines have double digit GB/s I/O speeds to RAM. I have no idea why you think it's not fast...

Buffered disk reads are your actual disk read speed. All the above you had is ram caching and therefore useless data.

What you said in the other thread was 300 mbps. The little "b" means bit. 300 Mb/s = 37.5 MB/s, which is normal for USB 2.0. You MUST pay attention to "b" (bit) vs "B" (byte) when talking about data size and I/O speeds.