Date: Thu, 19 Jun 2003 10:06:44 -0700 From: "Jin Guojun [NCS]" <j_guojun@lbl.gov> To: Petri Helenius <pete@he.iki.fi> Cc: Scott Long <scottl@freebsd.org> Subject: Re: freebsd-performance Digest, Vol 4, Issue 7 Message-ID: <3EF1EDA4.CBC4559@lbl.gov> References: <20030614190033.7F0DE37B407@hub.freebsd.org><20030615091254.M85497@bluhayz.org> <3EF0B507.2B1B6FDF@lbl.gov> <002101c335d9$f6664a20$812a40c1@PETEX31> <3EF0EABC.E9D75759@lbl.gov> <042501c33630$115159a0$812a40c1@PETEX31>
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Petri Helenius wrote:
> > But this seems to have different problem. At least write to RAID 1 requires
> > twice bus bandwidth for soft RAID 1. So, read should be faster than write.
> > But current read is 67 MB/s, write is 10 MB/s. Something is not working.
>
> Might be that whatever you´re using for the write waits for the second write
> to complete before it issues a write on the first drive again. vinum does this,
> it does not dispatch both writes at the same time. (I argued about this
> being "broken" for a while but then gave up, I understand why doing
> this differently does complicate the code, but at the same time improves
> performance)
The interesting thing is that the first write is fast every time I rebuilt file
system (newfs).
The write on soft RAID is about 3# MB/s. After a few large files on the file system,
the write speed drops to 11-12 MB/s. Sooner or later, the write speed will stay at
9-10 MB/s.
multiple writes will be lower around 8-9 MB/s (aggregated rate).
The initial hardware RAID write rate is about 15 MB/s. This may be due to the
battery backup write cache does no function correctly. The driver spits follwoing
message at the same time:
**Monitor** - Battery Fully Changed
...
**Monitor** ERROR - Low Battery
This may mean that cache is disbaled.
-Jin
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