Hello Mike,

I am very appreciate for your instruction.
Now I can  set hw_max_sectors through targcli when i create the device. I 
set it to 8192 same as raw rbd device.
The performance improve a little, 4M seq write increase from 24MB/s to 
40MB/s.(hw_max_sectors 64->8192, it is a /backstore/user:rbd/disk_xxx 
But it is far away from block device, if I usr /backstore/block 4M seq 
write it will be 500MB/s, performance is still a big problem.(first I 
should map a rbd device , then export  it by targetcli)

The performance difference between /backstore/user:rbd/ and 
/backstore/block is so big, is it normal?
Could you give me some suggestions about improving the performance of 
 /backstore/user:rbd/ device.

Thanks very much!

在 2018年9月3日星期一 UTC+8上午10:31:48,3kbo...@gmail.com写道:
> Hello Mike,
> Thank you for your informative response.
> 在 2018年8月28日星期二 UTC+8上午8:49:46,Mike Christie写道:
>> On 08/21/2018 08:52 PM, 3kbo...@gmail.com wrote: 
>> > Hi folks, 
>> > 
>> > I am newbie to open-iscsi. 
>> > My case is I export ceph rbd by open-iscsi. 
>> > 
>> > I found the max_sectors_kb is 64, the value is so small, and 4M 
>> sequence 
>> > write is only about 10MB/s. 
>> > I can not increase max_sectors_kb, if I do it will return "bash: echo: 
>> > write error: Invalid argument"(But I can change the value to a small 
>> one 
>> > < 64, max_hw_sectors_kb is 32767) 
>> > 
>> In new version of the linux kernel the initiator will use the optimal 
>> value reported by the target and then uses the max reported as the limit 
>> that the user can set. It sounds like you are using rbd/ceph with 
>> tcmu-runner which has a default limits of 64K. 
> Yes, I am using  tcmu-runner and gwcli.
>> If you are using targetcli/lio directly then you can set hw_max_sectors 
>> through targcli when you create the device or in the saveconfig.json 
>> file. 
>> If you are using the ceph-iscsi tools then I am actually working on a 
>> gwcli command to configure this right now. 
> Yes, I am using  ceph-iscsi tools.How can I change the limit by ceph-iscsi 
> tools?
> Thanks.

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