[lustre-discuss] dd oflag=direct error (512 byte Direct I/O)

[김형근]

Hi.
It's a pleasure to meet you, the lustre specialists.
(I do not speak English well ... Thank you for your understanding!)


I used the dd command in lustre mount point. (using the oflag = direct option)


------------------------------------------------------------
dd if = / dev / zero of = / mnt / testfile oflag = direct bs = 512 count = 1
------------------------------------------------------------


I need direct I / O with 512 byte block size.
This is a required check function on the software I use.


But unfortunately, If the direct option is present,
bs must be a multiple of 4K (4096) (for 8K, 12K, 256K, 1M, 8M, etc.) for operation.
For example, if you enter a value such as 512 or 4095, it will not work. The error message is as follows.


'error message: dd: error writing [filename]: invalid argument'


My test system is all up to date. (RHEL, lustre-server, client)
I have used both ldiskfs and zfs for backfile systems. The result is same.




My question is simply two.


1. Why does DirectIO work only in 4k multiples block size?
2. Can I change the settings of the server and client to enable 512bytes of DirectIO?


I wait for your answer. Thank you.
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