[mythtv-users] Why RAID 5 stops working in 2009

Yan Seiner yan at seiner.com
Fri Oct 24 17:18:17 UTC 2008


On Fri, October 24, 2008 10:12 am, John Drescher wrote:
>> I will, but I'm still a few months out most likely. I don't think you
>> would
>> be able to add disks to the individual raidz, you would create a new one
>> in
>> the pool. So you will have a second parity disk, but that's a good thing
>> with a 20 disk RAID. I'd probably put 5 disks in each raidz and put the
>> 4
>> raidz devices into a single pool. Then create the filesystems on top of
>> all
>> that. Then you can lose any 1 disk in each 5-disk raidz before losing
>> data.
>>
>> This is all based on reading the docs, I haven't tried it myself on real
>> hardware yet. If you have zfs-fuse installed, you can use files as the
>> block
>> devices in ZFS (loopback filesystem images). So you can do this testing
>> yourself on your intended platform. I might try it in VMWare myself now
>> that
>> I think about it. :)
>>
>
> Has performance drastically improved in the last year with the
> zfs-fuse module? I tried it back then and got hdparm reads and dd
> writes of less than 20MB/s on an array that does 250 MB/s+ writes.

Well, 0.5.0 is out.  Maybe the performance is better.  In my case, I'm not
really concerned about performance; I have a 15K SCSI subsystem with RAID1
and RAID0 partitions for speed, a RAID6 SATA disk subsystem for those
'normal' speed files, and this latest array will be through SATA port
multipliers so I expect lousy performance anyway.  I'm looking for a cheap
place to dump lots of data that is not accessed very often.

--Yan


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