Date: Tue, 27 May 2008 02:36:43 +1100 From: "Alexander Goncharov" <alexander.gsander@gmail.com> To: freebsd-scsi@freebsd.org Subject: Re: Strange behavior of SCSI RAID 10 (FreeBSD, LSILogic MegaRAID) Message-ID: <5c29cc10805260836rb8ccac0ic722c255e60286f8@mail.gmail.com> In-Reply-To: <20080526141005.GC1142@in-addr.com> References: <5c29cc10805260541r1f90f516q8ac7d45d2bb15702@mail.gmail.com> <20080526141005.GC1142@in-addr.com>
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On Tue, May 27, 2008 at 1:10 AM, Gary Palmer <gpalmer@freebsd.org> wrote: > On Mon, May 26, 2008 at 11:41:56PM +1100, Alexander Goncharov wrote: > > Hello world, I have faced with following issue on my dedicated server: > > > > 8x Opteron 885, 32gm RAM, 8x36 GM 15k rpm SCSI with RAID 10 > > > > FreeBSD 7.0-generic, 64 bit version > > > > > > > > IO performance and behavior is very strange: > > > > 1) No other process are running: > > > > Memory stat: > > > > Mem: 8796K Active, 9372K Inact, 80M Wired, 36K Cache, 12M Buf, 31G Free > > > > Copy 3GB file first time > > > > dd if=/home/3gb_file of=/home/3gb_file2 > > 6291456+0 records in > > 6291456+0 records out > > 3221225472 bytes transferred in 138.842926 secs (23200501 bytes/sec) > > > > 20MBS is very poor? > > > > Memory stat now: > > > > Mem: 8940K Active, 5951M Inact, 287M Wired, 36K Cache, 214M Buf, 25G Free > > > > 2) Copy the same file again: > > > > dd if=/home/3gb_file of=/home/3gb_file2 > > 6291456+0 records in > > 6291456+0 records out > > 3221225472 bytes transferred in 30.433515 secs (105844674 bytes/sec) > > > > 100MBs ? much better > > > > The "Inact" (Inactive) went up - the 3GiB file is now cached in > memory. So the second (and subsequent) runs are going from cached > memory so your 100MiB/sec transfer is actually just testing write > speed, not read/write speed. This is the same for your other > tests too > > "Inact" is memory that has been used and is being kept around incase > it is used again, in other words its caching file data in the > "Inact" region in top. It'll be reused if something else needs > the memory, but until then it sticks around. > > Remember - you are copying the file from and to the same > filesystem - this is always going to appear slow relative to > pure read or pure write tests. A pure write test is effectively > what you have when you're getting your 100MiB/sec test result since > its just writing out from cache memory. > > Regards, > > Gary > Hi Gary, Big thanks for your quick reply. Read only and write only speed is good ~100MBs. But I am not sure if it really good for hw RAID 10 8x 15k rpm drives. I am worried about read/write speed usecase which is most used at real tasks (data base). I was surprised 20 MBs speed, this value is likely to one drive speed. But I have 8 high speed drives. Something isn't right here. I am waiting for freebsd community help. Thanks in advance. Alexanderhome | help
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