[vdr] mdadm software raid5 arrays?

Simon Baxter linuxtv at nzbaxters.com
Fri Nov 6 19:38:03 CET 2009


Hi

I've been running logical volume management (LVMs) on my production VDR box 
for years, but recently had a drive failure.  To be honest, in the ~20 years 
I've had PCs in the house, this is the first time a drive failed!

Anyway, I've bought 3x 1.5 TB SATA disks which I'd like to put into a 
software (mdadm) raid 5 array.

I've found a few sites which talk about performance tuning, such as 
increasing the read-ahead from 128k:
echo 1024 > /sys/block/sda/queue/read_ahead_kb

And adjusting queue and scheduler depths:
#default 128
echo 256 > /sys/block/sda/queue/nr_requests
#default 256
echo 128 > /sys/block/sda/device/queue_depth

And running cfq as the scheduler:
echo cfq  > /sys/block/sda/queue/scheduler


But does anyone have any production VDR experience with mdadm - good or bad?

I regularly record 3 and sometimes 4 channels simultaneously, while watching 
a recording.  Under regular LVM, this sometimes seemed to cause some "slow 
downs".

My machine is a x86 64 bit dual core AM2, running on a Gigabyte motherboard.


Thanks
Simon 




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