[mythtv-users] OT: Troubleshooting write speed problems
Nathan A. Smith
nasa01 at comcast.net
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,
Back with some more info:
/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
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