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Re: [Xen-devel] 4.2.1: Poor write performance for DomU.



On 24/03/13 18:12, Steven Haigh wrote:
In fact, I just thought of something else.... I have an eSATA caddy that
connects to the same SATA controller. With this, I can slot any SATA
drive into it - and I should easily be able to pass this to any DomU.

I'll throw in a 1Tb SATA drive do that I don't have to break the
existing RAID6 array - as the testing on this drive can be destructive
testing - as otherwise the drive is blank.

Disk info:
Model Family:     Seagate Barracuda 7200.12
Device Model:     ST31000528AS
Serial Number:    9VP3BE9W
LU WWN Device Id: 5 000c50 01a238fd0
Firmware Version: CC49
User Capacity:    1,000,203,804,160 bytes [1.00 TB]
Sector Size:      512 bytes logical/physical

Results...

Dom0 (host machine):
# dd if=/dev/zero of=/dev/sdi bs=1M count=4096 oflag=direct
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 33.6909 s, 127 MB/s

Created an ext4 filesystem on /dev/sdi1...
# mkfs.ext4 -j /dev/sdi1

Run bonnie++ on the filesystem:
# mount /dev/sdi1 /mnt/esata
# cd /mnt/esata/
# bonnie++ -u 0:0
Version 1.96 ------Sequential Output------ --Sequential Input- --Random- Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP xenhost.lan.crc. 2G 433 95 119107 22 36723 7 960 95 145026 12 191.9 4 Latency 33231us 39824us 211ms 31466us 17459us 5073ms Version 1.96 ------Sequential Create------ --------Random Create-------- xenhost.lan.crc.id. -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete-- files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP 16 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++ Latency 285us 642us 315us 217us 349us 127us

We get ~145Mb/sec block read, ~119Mb/sec block write.

Now, lets pass the whole device through to a DomU.
# xm block-attach zeus.vm phy:/dev/sdi xvdc w

From the DomU now:
Firstly, the same dd as above:
# dd if=/dev/zero of=/dev/xvdc bs=1M count=4096 oflag=direct
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 33.6708 s, 128 MB/s

Create the ext4 filesystem again:
# mkfs.ext4 -j /dev/xvdc1

Run bonnie++ on the DomU:
Version 1.96 ------Sequential Output------ --Sequential Input- --Random- Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP zeus.crc.id.au 2G 387 99 121891 24 47759 14 992 98 141103 17 248.9 7 Latency 40518us 126ms 152ms 47174us 30061us 250ms Version 1.96 ------Sequential Create------ --------Random Create-------- zeus.crc.id.au -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete-- files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP 16 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++ Latency 174us 839us 2249us 113us 42us 185us

Interesting. We're at almost full speed in the DomU. 121Mb/sec write, 141Mb/sec read.

So my wonder is now... Why when put in a RAID6 do we have a 180Mb/sec+ from the Dom0, but only 50Mb/sec from the DomU of the same filesystem...

Any further testing that may indicate something?

--
Steven Haigh

Email: netwiz@xxxxxxxxx
Web: https://www.crc.id.au
Phone: (03) 9001 6090 - 0412 935 897
Fax: (03) 8338 0299

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