Re: [PATCH] scsi: sd: Keep the discard mode stable
From: Li Feng
Date: Wed Jun 19 2024 - 02:59:29 EST
> 2024年6月18日 16:47,Benjamin Block <bblock@xxxxxxxxxxxxx> 写道:
>
> On Tue, Jun 18, 2024 at 11:06:13AM +0800, Li Feng wrote:
>>> 2024年6月18日 00:26,Benjamin Block <bblock@xxxxxxxxxxxxx> 写道:
>>> On Sat, Jun 15, 2024 at 12:03:47AM +0800, Li Feng wrote:
>>>> There is a scenario where a large number of discard commands
>>>> are issued when the iscsi initiator connects to the target
>>>> and then performs a session rescan operation.
>>>
>>> Is this with just one specific target implementation? This sounds like a
>>> broken/buggy target, or is there a reason why this happens in general?
>>>
>>> And broken target sounds like device quirk, rather than impacting every
>>> possible target.
>>
>> This is a common problem. Before sending a rescan, discard has been
>> negotiated to UNMAP. After the rescan, there will be a short window for
>> it to become WS16, and then it will immediately become UNMAP.
>> However, during this period, a small amount of discard commands
>> may become WS16, resulting in a strange problem.
>
> Ok, interesting. Do you know why this short window happens?
I have explained it in other emails, you can read them.
Thanks,
Li
>
>>>> There is a time
>>>> window, most of the commands are in UNMAP mode, and some
>>>> discard commands become WRITE SAME with UNMAP.
>>>>
>>>> The discard mode has been negotiated during the SCSI probe. If
>>>> the mode is temporarily changed from UNMAP to WRITE SAME with
>>>> UNMAP, IO ERROR may occur because the target may not implement
>>>> WRITE SAME with UNMAP. Keep the discard mode stable to fix this
>>>> issue.
>>>>
>>>> Signed-off-by: Li Feng <fengli@xxxxxxxxxx>
>>>> ---
>
> --
> Best Regards, Benjamin Block / Linux on IBM Z Kernel Development
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