I read something in passing while googling last night, specifically about older versions of ext3 in linux not being very smart with respect to "burst length", i.e. exceeding 4MB - didn't store the link <doh!> [edit] found it! [/edit]
Tony / Ralph, could this have anything to do with slowdown on write to HDD in NASLite? e.g. if a RAID card is using a 64kB stripe then 64kB would be optimal, 4MB would totally overload the card.
I'm just thinking out loud.......
Code:
> I guess it depens on your definition of "trouble". These
> are benchmarks I ran on this system with the 2 3wares in
> hardware RAID5 and a software RAID0 across them:
> write read
> ----- ----
> ext2 81 180
> ext3 34 222
> XFS 109 213
> That ext3 write speed was something I just wasn't willing
> to live with on a system that used to perform so much
better
> (running RH7.3, hw RAID, and XFS).
That's because the 3Ware Escalade 7000-8000 series only have
1-4MB of SRAM. The Ext3 journal logic is rather "dumb"
(especially on old kernel 2.4) and bursts _more_ than 4MB at
a time. As a result, you overflow the small SRAM cache of
the 7000-8000 series, and the XOR stalls.
Newer Ext3 journaling code in newer 2.4/2.6 kernels is a
little better, but I still do _not_ recommend you use RAID-5
on the 7000/8000 series. I have repeatedly recommended
RAID-10 for 3Ware Escalade 7000-8000 series.
I'm still holding off on recommending the 3Ware Escalade
9500S for RAID-5, although most people are seeing good
performance with the 9.2.1.1 firmware released ~9 months ago.
The verdict is still out on the far newer 9550SX series
(with PowerPC).
Lastly, and quite repeatedly, the 3Ware card does _not_ offer
hot-swap capability when you use JBOD modes. I, among
countless others, have been saying this for years. You have
to use _another_ kernel facility to "hide" the status of the
discs when you're using JBOD modes.
found at:
http://lists.centos.org/pipermail/cento ... 58758.html
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