Mkfs command hangs while creating a new filesystem.

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本文介绍了解决在Red Hat Enterprise Linux (RHEL) 6和7上使用mkfs.xfs和mkfs.ext4命令创建LVM卷文件系统时出现的挂起问题。通过使用-K选项禁用块丢弃，可以避免由于不支持的存储设备导致的系统调用ioctl()失败。

https://access.redhat.com/solutions/727333

SOLUTION 已验证 - 已更新 2019年四月25日07:19 -

English

环境

Red Hat Enterprise Linux (RHEL) 6
Red Hat Enterprise Linux (RHEL) 7

问题

Both the mkfs.xfs and the mkfs.ext4 command stall on the ioctl() system call while trying to create a new file system on an lvm volume.
The machine appears to hang, and does not respond

决议

In order to create the filesystem use the -K option with mkfs command. It will disables the block discard at creating time. More information on mkfs man page:

Raw

        -K     Keep,  do  not  attempt  to discard blocks at mkfs time
                      (discarding blocks initially is useful on  solid  state
                      devices and sparse / thin-provisioned storage).

Example:

Raw

# mkfs.ext4 -K </dev/mapper/path_to_lvm_volume>   # For ext4 filesystem
# mkfs.xfs -K </dev/mapper/path_to_lvm_volume>      # For XFS filesystem

根源

The mkfs command issues a block discard command on the disk, but the underlying storage device cannot handle it.

诊断步骤

Collect the strace logs for mkfs command:

Raw

       # strace -f -tt -y -T -v -x -o /tmp/mkfs.out -s 4096  <mkfs command>

The strace logs for mkfs.xfs or mkfs.ext4 command shows that the command is hanging after issuing the ioctl 0x1277:

Raw

        $ tail  -2  mkfs.txt 
        1538  08:59:41.724086 write(1, "\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08", 13) = 13 <0.000053>
        1538  08:59:41.724209 ioctl(3, 0x1277           <-------- hung after this
        [...]

From the kernel source, 0x1277 ioctl corresponds to BLKDISCARD:

Raw

        include/linux/fs.h:
        ------------------
        344 #define BLKDISCARD _IO(0x12,119)
        [...]

The mkfs command was issuing a block discard command to the disk but the disk device did not support the command, which caused the IO errors observed in first snip, which were then being logged.