为提高效率，提问时请提供以下信息，问题描述清晰可优先响应。
- 【TiDB 版本】：4.0.0-RC
- 【问题描述】：在BR导出数据的时候报Error: msg:“Io(Os { code: 22, kind: InvalidInput, message: “Invalid argument” })”
执行的语句
./br backup full --pd "10.204.54.85:2379" --storage "local:///data_bak" --ratelimit 120 --log-file backupfull.log
日志中打印的错误
[2020/05/18 15:27:40.282 +08:00] [INFO] [client.go:402] ["backup started"] [StartKey="dIAAAAAAAABvX3IAAAAAAAAAAA=="] [EndKey="dIAAAAAAAABvX3L//////////wA="] [RateLimit=125829120] [Concurrency=4]
[2020/05/18 15:27:40.283 +08:00] [INFO] [push.go:29] ["new backup client"]
[2020/05/18 15:27:40.284 +08:00] [INFO] [client.go:721] ["try backup"] ["backup request"="{\"cluster_id\":6714244546456264833,\"start_key\":\"dIAAAAAAAABvX3IAAAAAAAAAAA==\",\"end_key\":\"dIAAAAAAAABvX3L//////////wA=\",\"end_version\":416753086478680158,\"rate_limit\":125829120,\"concurrency\":4,\"storage_backend\":{\"Backend\":{\"Local\":{\"path\":\"/data_bak\"}}}}"]
[2020/05/18 15:27:40.284 +08:00] [INFO] [client.go:721] ["try backup"] ["backup request"="{\"cluster_id\":6714244546456264833,\"start_key\":\"dIAAAAAAAABvX3IAAAAAAAAAAA==\",\"end_key\":\"dIAAAAAAAABvX3L//////////wA=\",\"end_version\":416753086478680158,\"rate_limit\":125829120,\"concurrency\":4,\"storage_backend\":{\"Backend\":{\"Local\":{\"path\":\"/data_bak\"}}}}"]
[2020/05/18 15:27:40.285 +08:00] [INFO] [client.go:721] ["try backup"] ["backup request"="{\"cluster_id\":6714244546456264833,\"start_key\":\"dIAAAAAAAABvX3IAAAAAAAAAAA==\",\"end_key\":\"dIAAAAAAAABvX3L//////////wA=\",\"end_version\":416753086478680158,\"rate_limit\":125829120,\"concurrency\":4,\"storage_backend\":{\"Backend\":{\"Local\":{\"path\":\"/data_bak\"}}}}"]
[2020/05/18 15:27:40.286 +08:00] [INFO] [client.go:733] ["backup streaming finish"] [StoreID=1]
[2020/05/18 15:27:40.286 +08:00] [INFO] [client.go:733] ["backup streaming finish"] [StoreID=5]
[2020/05/18 15:27:40.476 +08:00] [INFO] [client.go:740] ["range backuped"] [StartKey="dIAAAAAAAABvX3IAAAAAAAAAAA=="] [EndKey="dIAAAAAAAABvX3L//////////wA="]
[2020/05/18 15:27:40.476 +08:00] [INFO] [client.go:733] ["backup streaming finish"] [StoreID=4]
[2020/05/18 15:27:40.476 +08:00] [ERROR] [push.go:111] ["backup occur unknown error"] [error="Io(Os { code: 22, kind: InvalidInput, message: \"Invalid argument\" })"] [stack="github.com/pingcap/log.Error\
\t/go/pkg/mod/github.com/pingcap/log@v0.0.0-20200117041106-d28c14d3b1cd/global.go:42\
github.com/pingcap/br/pkg/backup.(*pushDown).pushBackup\
\t/home/jenkins/agent/workspace/build_br_multi_branch_v4.0.0-rc/go/src/github.com/pingcap/br/pkg/backup/push.go:111\
github.com/pingcap/br/pkg/backup.(*Client).BackupRange\
\t/home/jenkins/agent/workspace/build_br_multi_branch_v4.0.0-rc/go/src/github.com/pingcap/br/pkg/backup/client.go:424\
github.com/pingcap/br/pkg/backup.(*Client).BackupRanges.func2\
\t/home/jenkins/agent/workspace/build_br_multi_branch_v4.0.0-rc/go/src/github.com/pingcap/br/pkg/backup/client.go:337"]
[2020/05/18 15:27:40.476 +08:00] [INFO] [client.go:394] ["backup range finished"] [take=193.818569ms]
[2020/05/18 15:27:40.476 +08:00] [INFO] [client.go:329] ["Backup Ranges"] [take=193.978007ms]
[2020/05/18 15:27:40.478 +08:00] [INFO] [ddl.go:407] ["[ddl] DDL closed"] [ID=f3b4fd37-2134-4760-b186-1adc33e0e973] ["take time"=1.866057ms]
[2020/05/18 15:27:40.478 +08:00] [INFO] [ddl.go:301] ["[ddl] stop DDL"] [ID=f3b4fd37-2134-4760-b186-1adc33e0e973]
[2020/05/18 15:27:40.480 +08:00] [INFO] [domain.go:607] ["domain closed"] ["take time"=4.354146ms]
[2020/05/18 15:27:40.481 +08:00] [INFO] [collector.go:180] ["Full backup Failed summary : total backup ranges: 1, total success: 0, total failed: 1"] ["backup total regions"=2359] [unitName="range start:74800000000000006f5f720000000000000000 end:74800000000000006f5f72ffffffffffffffff00"] [error="msg:\"Io(Os { code: 22, kind: InvalidInput, message: \\\"Invalid argument\\\" })\" "] [errorVerbose="msg:\"Io(Os { code: 22, kind: InvalidInput, message: \\\"Invalid argument\\\" })\" \
github.com/pingcap/br/pkg/backup.(*pushDown).pushBackup\
\t/home/jenkins/agent/workspace/build_br_multi_branch_v4.0.0-rc/go/src/github.com/pingcap/br/pkg/backup/push.go:113\
github.com/pingcap/br/pkg/backup.(*Client).BackupRange\
\t/home/jenkins/agent/workspace/build_br_multi_branch_v4.0.0-rc/go/src/github.com/pingcap/br/pkg/backup/client.go:424\
github.com/pingcap/br/pkg/backup.(*Client).BackupRanges.func2\
\t/home/jenkins/agent/workspace/build_br_multi_branch_v4.0.0-rc/go/src/github.com/pingcap/br/pkg/backup/client.go:337\
runtime.goexit\
\t/usr/local/go/src/runtime/asm_amd64.s:1357"]
