RAID5 write performance and Hauppaugge 250 transfer size

[pez]

I just built a software RAID5 array and for small transfer sizes the write performance is very bad. ATTO DisK Benchmarks show write transfers below 16KB to be less than 5MB/s and at 2KB to be less than 1MB/s.

On the other hand write transfer of 128KB are 12MB/s and 256KB and greater are 18MB/s.

Does any one know what transfer size the Hauppaugge PVR250 drivers uses? I'm using driver version 1.18.21.22266 dated 9/22/2004 if that help.

BTW the read performance is very good, over 80MB/s for transfers 16KB and greater.

thanks,
pez

[mdmint]

I believe the data from hardware encoding tuner is streamed, not in blocks, and the rate will of course depend on record quality. Don't know for sure. Best thing you can do is simply test your system.

RAID5 inherently takes a hit on write performance do to parity calculation before writing data. I don't use software RAID5 but can tell you even with a decent Escalade 9500 without controller write back cache enabled (something IRRC a software solution can't do) it can't keep up with 5 max quality recordings and 3 Client playbacks simultaneously, playback is jumpy. With write back cache enabled no problem.

[pez]

Sure, the conexant chip may send data over PCI (in bursts) to the driver which saves the data in a memory buffer. However, when data is written to a harddrive, the OS must allocate room for it before sending the data. I think the smallest amount it can allocate is a sector (512b).

Does the driver look for the cluster size of the filesystem and match its buffer to that? Or does the driver make an OS call and the OS controls the buffering of data?

Interesting about your RAID5 setup if MAX is 12Mbits/s the your write performance is less than 8MB/s w/o caching but while reading less than 5MB/s. That would indicate that the driver is attempting to write small chunks of data and the cache is combining it into bigger chunks to make the write more efficient.

I think I will test a simultaneous copy from a standard disk to the raid array and vise versa.

thanks,
-pez

[mikesm]

Are you running software raid 5 on windows? if so, no wonder you have problems. Hardware raid is the only way to go on Windows. If you ran Linux though, you'll find software raid works really well, and if you use a high performance filesystem like XFS, and avoid PCI bottlenecks, you can almost max out a gigabit ethernet...

Thanks,
Mike

[mdmint]

Huh, you lost me? I said tested 5 concurrent MaxQ recording with simutaneous Client playback of 3 previously recorded streams. EACH MaxQ would be 12Mbps rate, not total 12Mbps, for total 60Mbs write stream.

As far as driver/OS calls etc for record stream don't know, haven't researched it and doesn't matter to me. What matters was/is can the system keep up as needed under maximum anticipated HD subsystem load: 5 recording sessions with 3 playback sessions? Yes.

[pez]

60Mbs = 7.5MB/s. Big B is Byte, little b is bit.

[pez]

well, i did a copy test to check performance before i start experimenting with sage. I created 3 x 600MB files on the RAID5 array and 2 x 600MB files on the OS disk. I simultaneously copied the 2 files to the RAID and the the 3 files to the OS.

It took 300s to copy the 2 files, which finished within 5s of each other. And, it took 280s to copy the 3 files, which finished within 10s of each other. 1200MB/300s = 4MB/s for dual write, during a 1800MB/280s = 6.4MB/s for triple read.

Now this also test the disk performance of the OS disk which mostlikely supples data differently than the encoder cards. However, these results make me kinda curious on how ATTO gets such high read speeds.

too bad winblows doesn't allow you to configure a disk cache in main memory. This is the reason I would really like sage to announce if they are indeed going to have a linux port for us, and what dist it is. Then i could just use linux sw raid with my windows encoder for now, and switch the encoders to linux when that's available.

-pez

[stanger89]

As a data point:
8x250GB (3ware 7506-8) -> GB network -> WD Raptor (10k 74GB):
5.06GB/250sec ~= 21MB/sec (168Mbps)
Raptor -> network -> 3ware
5.06GB/160sec ~= 32MB/sec (260Mbps)

That would be a RAID-5 array.

[pez]

Thanks, Stanger89. That's pretty impressive.

As others might be interested in the Windows SW Raid-5 option, here's my config.

5x250GB Disks (3 Maxtors, 1 Hitachi, 1 WD)
4 disks on 2xPromise Ultra133 TX2 (could not get 3 working)
1 disk on the onboard HighPoint 370
yields 932GB of disk space at a cost of $460 (3 disks came with the ultra133 tx2 cards).

[pez]

Oh one more thing. When I did the test, the CPU usage fluxuated between 12% and 33% on a 2.16GHz P4 w/ 1GB PC2700. Interestingly enough, when the dual write tests yielded a higher CPU utilization than the dual write with triple read.

[dvd_maniac]

I have the Promise sx4060 with 4x400GB /133 drives. I had it in another thread where I started having serious write problems after trying to resize the partition, so instead of trying to fix it (OS & programs re-install) I decided to pick up the 3ware 9500s-8 Sata raid card and 4x300GB Sata drives.

Now from what I am reading this is true hardware where the 4060 was not?

So what kind of speed inprovements can I expect from this new card? Giving that both cards are going through the same PCI 2.2 interface was I already maxed out with the slower Promise card?

[stanger89]

Well I get about 32MB/sec writes to my 7506-8 over my Gigabit network. I can write 5GB in about 3 min.

[dvd_maniac]

That is a IDE card right? If so, is the SATA cards actually "REAL WORLD" faster? Or does the PCI bandwidth limit it anymore then the IDE? Also, how many drives do you have hooked up?

[stanger89]

No SATA is not appreciably faster, the HDDs are still the bottleneck. Figure, 100-125 MB/sec for the PCI bus, HDDs top out at about 50MB/sec each.

I've got 8 drives in that array, RAID-5.

[dvd_maniac]

Thanks Stanger.
That should at least be sufficient for 5 tuners recording at 12mbit/s and a total of three clients. Plus I am glad I am upgrading simply because the Sata cables make it a little cooler and easier to work in the case.

Again, thanks for all your Raid info here and here

You saved me from buying a whole new system and instead just upgrade my raid card. This 3ware 9500s-8 is way cool.