[mythtv-users] Samba 3 better than NFS 3 for recording over Ethernet

Brad DerManouelian myth at dermanouelian.com
Thu Dec 29 11:32:30 EST 2005

On Dec 28, 2005, at 10:51 PM, Jarod Wilson wrote:

> On Wednesday 28 December 2005 22:37, Brad DerManouelian wrote:
>> On Dec 28, 2005, at 10:30 PM, Yeechang Lee wrote:
>>> To make a long story short, my 2.8TB JFS-on-LVM2-on-software RAID 5
>>> array has certain mysterious performance bottlenecks that result in
>>> 7.5-10MB/s local write speeds, despite eight spindles and two 3Ware
>>> 7506 controller cards in JBOD mode and on separate buses and with
>>> iowait never going above a few percentage points at the very
>>> most. Over the network that's even slower, of course.
>> This actually sounds pretty typical of RAID 5 to me. Every write
>> results in 2 simultaneous writes. Even slower when you're doing it in
>> software. Great for redundancy, terrible for throughput. That's the
>> trade-off.
> Erm, software RAID 5 isn't *that* bad. I've got a sw RAID 5 array  
> that only
> consists of four ATA drives, and can write at a sustained rate of  
> 30MB/s
> without a problem. I've got a 5-drive U320 software RAID 5 array in  
> another
> machine that does ~80MB/s without a problem.

My point is that RAID 5 is *MUCH* slower than just about any other  
RAID config and you should expect your max speed to be half of your  
fastest drive. Put those U320's on RAID 0+1 and you'll likely double  
your speed (and half your recoverability). That being said, the  
original poster obviously hasn't got that kind of throughput and RAID  
5 is cutting whatever he has in half.

Yeechang, what kind of drives are in your RAID 5? ATA-133? 7200 RPM?  
8MB Cache?


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