[mythtv-users] OT: Troubleshooting write speed problems

Wed Aug 22 00:13:50 UTC 2007

On Tue, 2007-08-21 at 13:30 +0000, nasa01 at comcast.net wrote: 
> -------------- Original message ----------------------
> From: Joel Michael <joel at gimps-r-us.com>
> > nasa01 at comcast.net wrote:
> > > Hi,
> > > 
> > > I know, this is way off topic, but I figured there must be a lot of smarter 
> > people on the list than I.
> > > I was troubleshooting what I thought was a network issue, when I decided to 
> > test my harddrive speeds... Looking at the results, my aim how changed.  How do 
> > I fix these write speed issues?  Info follows:
> > > 
> > Ok, I'll throw in a few comments from what I'm seeing.  This post isn't 
> > exactly easy to follow, but I'll try and make the most of it.
> > 
> > >  I have three machines (Main, mythtv, MythTV_Server).  All machines are 
> > running a version of mandrake (later than 2006).  
> > > 
> > I'm not too familiar with Mandrake, but a linux kernel is a linux kernel ;-)
> > 
> > > mythtv:
> > > Kernel:  2.6.22-rc1
> > > 
> > YIKES!  Is there any particular reason you're running a -rc1 kernel, 
> > especially a -rc1 from the last stable kernel?  You should probably be 
> > running 2.6.22 (maybe 2.6.22.something), or the latest 2.6.23-rc 
> > (whatever it might be at this moment in time).  Just to make sure, does 
> > 'uname -r' say 2.6.22-rc1?
> > 
> > > GIGABYTE GV-NX73G256D-RH GeForce 7300GS 512MB(256MB on Board) GDDR2 PCI 
> > Express x16 Video Card 
> > > WINTEC AMPO 1GB (2 x 512MB) 240-Pin DDR2 SDRAM DDR2 533 (PC2 4200) Dual 
> > Channel Kit Desktop Memory Model 3AMD2533-1G1K-R 
> > > AMD Athlon 64 X2 3800+(65W) Windsor 2.0GHz Socket AM2 Processor 
> > > Seagate ST3300831A ATA Drive
> > > MSI K9N Platinum Socket AM2 NVIDIA nForce 570 Ultra MCP ATX AMD Motherboard 
> > > 
> > > hdparm -v /dev/hda
> > > 
> > The other thing you may want to investigate is using libata to access 
> > your hard drives, but YMMV as PATA support isn't quite as mature as SATA 
> > support for some chipsets.
> > 
> > > multcount = 16(on)
> > > IO_Support = 1 (32-bit)
> > > unmaskirq = 1 (on)
> > > using_dma = 1 (on)
> > > keepsettings = 0 (off)
> > > readahead = 256 (on)
> > > geometry = 19457/255/63, sectors = 312581808, start = 0
> > > 
> > > dd results very similar to dd results for hda on MythTV_Server
> > > 
> > > 
> > ********************************************************************************
> > *********
> > > MythTV_Server:
> > > Kernel:  2.6.17-13mdv
> > > 
> > > HighPoint Technologies, RocketRaid 1740 
> > > DFI Infinity RS482 Motherboard 
> > > CPU AMD|A64 3400+ 2.2G 939 
> > > 756M generic ram 
> > > 4x320G Harddrives in Raid 5 
> > > 
> > > hdparm -v /dev/hda (same as mythtv, except for geometry)
> > > ...will update hdparm -v /dev/sda later (would this be usefull?)
> > > 
> > > hdparm -tT /dev/sda
> > > 
> > > /dev/sda:
> > >  Timing cached reads:   2432 MB in  2.00 seconds = 1214.37 MB/sec
> > >  Timing buffered disk reads:  184 MB in  3.01 seconds =  61.05 MB/sec
> > > 
> > > time dd if=/dev/zero of=./test.tmp bs=1024k count=4000
> > > 2066+0 records in
> > > 2066+0 records out
> > > 2166358016 bytes (2.2 GB) copied, 129.33 seconds, 16.8 MB/s
> > > Command terminated by signal 2
> > > 0.02user 19.98system 2:09.49elapsed 15%CPU (0avgtext+0avgdata 0maxresident)k
> > > 0inputs+0outputs (1major+275minor)pagefaults 0swaps
> > > 
> > > sync; time bash -c "dd if=/dev/zero bs=1024k count=20 48 
> > of=/mnt/Raid/testspeed; sync"
> > > 2048+0 records in
> > > 2048+0 records out
> > > 2147483648 bytes (2.1 GB) copied, 63.3346 seconds, 33.9 MB/s
> > > 0.01user 4.42system 1:13.53elapsed 6%CPU (0avgtext+0avgdata 0maxresident)k
> > > 0inputs+0outputs (4major+943minor)pagefaults 0swaps
> > > 
> > So, what I'm seeing here (and correct me if I'm wrong), is that the "dd" 
> > test isn't quite living up to the speed that hdparm suggests.
> > 
> > Off the top of my head, I can think of a few reasons for this.
> > 
> > First thing that comes to mind is disk contention.  Is there anything 
> > else doing a reasonable amount of I/O on the disk during your test?  To 
> > make sure, try booting to single user mode and re-run the dd test.
> > 
> > The next thing I can think of, is disk layout.  How is your disk 
> > partitioned?  Do you run LVM?  Software RAID?  On your RAID set, how big 
> > is the stripe size?
> > 
> > Next contender is the file system.  What kind of file system is it (for 
> > MythTV systems, people tend to use XFS)?  Did you remember to tell the 
> > file system about the stripe size of your RAID set?  What other 
> > performance related metrics did you adjust (e.g. block size, inodes per 
> > block, journal size, etc)?  What mount options are you using (e.g. 
> > noatime, journal options)?
> > 
> > Lastly, check the hardware (it's unlikely that hardware is a problem, 
> > given that you have two machines displaying the same symptoms).  Is your 
> > power supply ok?  Are all the cables plugged in right?  Are any of the 
> > cables kinked or pinched?  Do your kernel logs say anything about disk 
> > errors?  Controller errors?
> > 
> > A well optimised system will be within a few MB/sec of the theoretical 
> > throughput as reported by hdparm.  My Myth box is 2MB/sec under on a 
> > software mirror, and 10MB/sec under the sum of two disks on a RAID-0 set 
> > that is actually being used (for commflaging and recording at the 
> > moment, if you're wondering).
> > 
> > But, the biggest question is, is it really a problem?  Put on your 
> > normal load, then fire up iostat and take a look at the last 4 columns 
> > (avgqu-sz, await, svctm, %util).  You want avgqu-sz to usually be less 
> > than 10, certainly no more than 100.  The next two columns are only 
> > really useful if you're tuning for latency (which isn't much of a factor 
> > in a MythTV box, but can be for something like a home directory server). 
> >   The %util is good to look at as well, but can be a bit misleading. 
> > Don't worry too much if you're 100% utilised, but your queue size is 
> > still low.
> 
> Thanks Joel,
> 
> I do appreciate you taking the time out to respond.  I can't answer all your astute questions right now, as I'm at work -- however I will try and clear some things up...
> 
> 1.  I am using 2.6.22-rc1 because I have both a PVR-500 and a pchdtv 3500 in my system.  Recommendations were to use a kernel after 2.6.18 (as it has built in support for the 3500).  But 2.6.18 - 2.6.22 had some kind of bug which caused problems with ivtv -- rc1 was the first one to fix that bug.  I haven't updated since (maybe I should).
> 
> 2. Why care?  Mainly for my Server, which has all my media on it.  Putting new media on it (for example vob files) can be really slow (usaully around 25MB/s).  Playing dvd ripped files seems ok, but playing  hd files producing some *stuttering*.  I also have noticed some pauses in playing music from the server.  Finally, I hope to have access to media via multiple computer (all at once) which the present speeds wouldn't support.
> 
> 3.  HighPoint Technologies, RocketRaid 1740 is a pci hardware raid card (see http://www.highpoint-tech.com/ for info).  I don't run LVM and Nope - not software RAID.  The RAID array is configured as one partiton.  I am using JFS as the fs (can't remember why....)
> 
> Thanks again for taking the time,
> 
> nasa

Back with some more info:

/etc/fstab:

/dev/sda1 /mnt/Raid jfs defaults,noatime,rw 1 0

iostat output (after coping a vob file (4.4G)):

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.06    0.01    0.29    0.12    0.00   99.51

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
hda               0.55         1.44         5.44    2234830    8424085
sda               1.57        75.89        98.87  117473298  153046904

Nasa

> 
> 
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