Re: [zfs-discuss] Re: 3510 HW RAID vs 3510 JBOD ZFS SOFTWARE RAID

[Dave C. Fisk]

Hi Matthew, In the case of the 8 KB Random Write to the 128 KB recsize filesystem the I/O were not full block re-writes, yet the expected COW Random Read (RR) at the pool level is somehow avoided. I suspect it was able to coalesce enough I/O in the 5 second transaction window to construct 128 KB blocks. This was after all, 24 threads of I/O to a 2 GB file at a rate of  140,000  IOPS. However, when using the 8 KB recsize it was not able to do this.  I will check to see if it's fixed in b45. Thanks! Dave 8 KB  update to a 128 KB block), however, did not have much Random Read (RR) at the pool level. The 8 KB RW to the 8 KB recsize filesystem is where I generaly observed RR at the pool level. RR is Random Read, RW is random Write... Dave Matthew Ahrens wrote: On Wed, Aug 09, 2006 at 04:24:55PM -0700, Dave C. Fisk wrote: Hi Eric, Thanks for the information. I am aware of the recsize option and its intended use. However, when I was exploring it to confirm the expected behavior, what I found was the opposite! The test case was build 38, Solaris 11, a 2 GB file, initially created with 1 MB SW, and a recsize of 8 KB, on a pool with two raid-z 5+1, accessed with 24 threads of 8 KB RW, for 500,000 ops or 40 seconds which ever came first. The result at the pool level was 78% of the operations were RR, all overhead. For the same test, with a 128 KB recsize (the default), the pool access was pure SW, beautiful. I'm not sure what RR means, but you should re-try your tests on build 42 or later. Earlier builds have bug 6424554 "full block re-writes need not read data in" which will cause a lot more data to be read than is necessary, when overwriting entire blocks. --matt -- Dave Fisk, ORtera Inc. Phone (562) 433-7078 [EMAIL PROTECTED] http://www.ORtera.com

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