背景
我们通过docker的rexray插件来创建ceph rbd设备的docker volume，但总提示创建失败。
# docker volume create --driver=rexray --opt=size=5 --name=cephrbd-book
Error response from daemon: create test_cephrbd_volume: VolumeDriver.Create: {"Error":"Failed to create new volume"}
OS版本：
# lsb_release -a
LSB Version: :core-4.1-amd64:core-4.1-noarch
Distributor ID: CentOS
Description: CentOS Linux release 7.4.1708 (Core)
Release: 7.4.1708
Codename: Core
Ceph版本：
# ceph version
ceph version 0.94.5
rexray版本：
# rexray version
REX-Ray
-------
Binary: /usr/bin/rexray
Flavor: client+agent+controller
SemVer: 0.9.0
OsArch: Linux-x86_64
Branch: (detached from 2a7458d
Commit: 2a7458dd90a79c673463e14094377baf9fc8695e
Formed: Wed, 26 Jul 2017 14:35:37 CST
libStorage
----------
SemVer: 0.6.0
OsArch: Linux-x86_64
Branch: (detached from fa055d6
Commit: fa055d6da595602715bdfd5541b4aa6d4dcbcbd9
Formed: Wed, 26 Jul 2017 14:35:11 CST
分析
之前我们在ubuntu 16.04的环境中，也搭建过docker+ceph+rexray的环境，使用docker命令创建volume并没有报错。正常的流程是：
1. 创建docker volume：rexray会使用rbd create命令创建一个rbd设备；
2. 使用该volume创建docker 容器：rexray会将rbd 设备map到docker host上成为一个/dev/rbd设备，再使用mount命令将/dev/rbd设备挂载到/var/lib/libstorage/volumes/目录，供容器使用；
3. 删除该容器时：先umount掉/dev/rbd设备在/var/lib/libstorage/volumes/目录的挂载，再rbd unmap掉rbd设备在docker host上的映射；
4. 删除docker volume：rexray会使用rbd rm命令删除该rbd设备；
在我们的实际使用情况中，发现只有第一步会出错，后面的三步都并未出现任何异常。而且，如果我们不使用docker volume create命令创建rbd设备，而是直接使用“rbd create”命令来创建rbd设备，也并未出现任何错误，且该rbd设备也可以正常使用。这是很奇怪的一个地方。
查看docker日志，也只是提示“Failed to create new volume”，并没有其他有用的信息。
# journalctl -xu docker
...
Jan 22 10:45:13 dcos-agent2 dockerd[66886]: time="2018-01-22T10:45:13.937645601+08:00" level=error msg="Handler for POST /v1.29/volumes/create returned error: create cephrbd-book: VolumeDri
ver.Create: {"Error":"Failed to create new volume"}
"
既然docker中没有更有价值的日志，那么就尝试看下rexray的日志，这里需要打开rexray的debug选项(打开方法参考)，从而可以看到更多的日志。
# vim /var/log/rexray/rexray.log
...
time="2018-01-19T19:12:32+08:00" level=info msg=" -------------------------- HTTP REQUEST (CLIENT) -------------------------"
time="2018-01-19T19:12:32+08:00" level=info msg=" GET /volumes/rbd?attachments=0 HTTP/1.1"
time="2018-01-19T19:12:32+08:00" level=info msg=" Host: libstorage-server"
time="2018-01-19T19:12:32+08:00" level=info msg=" Libstorage-Instanceid: rbd=109.105.115.73"
time="2018-01-19T19:12:32+08:00" level=info msg=" Libstorage-Localdevices: rbd="
time="2018-01-19T19:12:32+08:00" level=info msg=" Libstorage-Tx: txID=b9fb044b-d47a-4ac5-7533-5824b8dc737a, txCR=1516360352"
time="2018-01-19T19:12:32+08:00" level=info msg=" "
time="2018-01-19T19:12:33+08:00" level=info
time="2018-01-19T19:12:33+08:00" level=info msg=" -------------------------- HTTP RESPONSE (CLIENT) -------------------------"
time="2018-01-19T19:12:33+08:00" level=info msg=" HTTP/1.1 200 OK"
time="2018-01-19T19:12:33+08:00" level=info msg=" Content-Length: 228"
time="2018-01-19T19:12:33+08:00" level=info msg=" Content-Type: application/json"
time="2018-01-19T19:12:33+08:00" level=info msg=" Date: Fri, 19 Jan 2018 11:12:33 GMT"
time="2018-01-19T19:12:33+08:00" level=info msg=" Libstorage-Servername: jade-chopper-ky"
time="2018-01-19T19:12:33+08:00" level=info msg=" "
time="2018-01-19T19:12:33+08:00" level=info msg=" {"
time="2018-01-19T19:12:33+08:00" level=info msg=" "rbd.test_fs_device2": {"
time="2018-01-19T19:12:33+08:00" level=info msg=" "name": "test_fs_device2","
time="2018-01-19T19:12:33+08:00" level=info msg=" "size": 16,"
time="2018-01-19T19:12:33+08:00" level=info msg=" "id": "rbd.test_fs_device2","
time="2018-01-19T19:12:33+08:00" level=info msg=" "type": "rbd""
time="2018-01-19T19:12:33+08:00" level=info msg=" },"
time="2018-01-19T19:12:33+08:00" level=info msg=" "rbd.test_majk": {"
time="2018-01-19T19:12:33+08:00" level=info msg=" "name": "test_majk","
time="2018-01-19T19:12:33+08:00" level=info msg=" "id": "rbd.test_majk","
time="2018-01-19T19:12:33+08:00" level=info msg=" "type": "rbd""
time="2018-01-19T19:12:33+08:00" level=info msg=" }"
time="2018-01-19T19:12:33+08:00" level=info msg=" }"
time="2018-01-19T19:12:33+08:00" level=info
time="2018-01-19T19:12:33+08:00" level=info msg=" -------------------------- HTTP REQUEST (CLIENT) -------------------------"
time="2018-01-19T19:12:33+08:00" level=info msg=" POST /volumes/rbd HTTP/1.1"
time="2018-01-19T19:12:33+08:00" level=info msg=" Host: libstorage-server"
time="2018-01-19T19:12:33+08:00" level=info msg=" Libstorage-Instanceid: rbd=109.105.115.73"
time="2018-01-19T19:12:33+08:00" level=info msg=" Libstorage-Localdevices: rbd="
time="2018-01-19T19:12:33+08:00" level=info msg=" Libstorage-Tx: txID=b1565614-1b5f-4de2-5756-b74fb99887aa, txCR=1516360353"
time="2018-01-19T19:12:33+08:00" level=info msg=" "
time="2018-01-19T19:12:33+08:00" level=info msg=" {"name":"cephrbd-book","availabilityZone":"","iops":0,"size":5,"type":"","opts":{"size":"5"}}"
time="2018-01-19T19:12:33+08:00" level=info
time="2018-01-19T19:12:33+08:00" level=info msg=" -------------------------- HTTP RESPONSE (CLIENT) -------------------------"
time="2018-01-19T19:12:33+08:00" level=info msg=" HTTP/1.1 500 Internal Server Error"
time="2018-01-19T19:12:33+08:00" level=info msg=" Content-Length: 319"
time="2018-01-19T19:12:33+08:00" level=info msg=" Content-Type: application/json"
time="2018-01-19T19:12:33+08:00" level=info msg=" Date: Fri, 19 Jan 2018 11:12:33 GMT"
time="2018-01-19T19:12:33+08:00" level=info msg=" Libstorage-Servername: jade-chopper-ky"
time="2018-01-19T19:12:33+08:00" level=info msg=" "
time="2018-01-19T19:12:33+08:00" level=info msg=" {"
time="2018-01-19T19:12:33+08:00" level=info msg=" "message": "Failed to create new volume","
time="2018-01-19T19:12:33+08:00" level=info msg=" "status": 500,"
time="2018-01-19T19:12:33+08:00" level=info msg=" "error": {"
time="2018-01-19T19:12:33+08:00" level=info msg=" "driverName": "rbd","
time="2018-01-19T19:12:33+08:00" level=info msg=" "inner": {"
time="2018-01-19T19:12:33+08:00" level=info msg=" "inner": "Error running command: [rbd: strict_strtoll: garbage at end of string. got: '5G'\n]","
time="2018-01-19T19:12:33+08:00" level=info msg=" "msg": "unable to create rbd""
time="2018-01-19T19:12:33+08:00" level=info msg=" },"
time="2018-01-19T19:12:33+08:00" level=info msg=" "opts.Size": 5,"
time="2018-01-19T19:12:33+08:00" level=info msg=" "volumeName": "cephrbd-book""
time="2018-01-19T19:12:33+08:00" level=info msg=" }"
time="2018-01-19T19:12:33+08:00" level=info msg=" }"
通过日志可以看到，每次发送docker volume create命令时，实际发送了两次http请求，第一次是列出当前的rbd设备，第二次才是发出post请求来创建一个rbd设备。而这里的日志，则给出了更多的信息“rbd: strict_strtoll: garbage at end of string. got: '5G'”。也就是说，很可能就是在rexray调用rbd create命令时发生了错误。这里，我们打开rexray源码继续跟踪，具体的源码文件为rexray/blob/master/libstorage/drivers/storage/rbd/utils/utils.go。
//RBDCreate creates a new RBD volume on the cluster
func RBDCreate(
ctx types.Context,
pool *string,
image *string,
sizeGB *int64,
objectSize *string,
features []*string) error {
cmd := exec.Command(
rbdCmd, "create", poolOpt, *pool,
"--object-size", *objectSize,
"--size", strconv.FormatInt(*sizeGB, 10)+"G",
)
for _, feature := range features {
cmd.Args = append(cmd.Args, "--image-feature")
cmd.Args = append(cmd.Args, *feature)
}
cmd.Args = append(cmd.Args, *image)
_, _, err := RunCommand(ctx, cmd)
if err != nil {
return goof.WithError("unable to create rbd", err)
}
return nil
}
根据上面的代码可以大致看出，rexray就是直接调用rbd create命令来创建rbd设备，和我们直接调用命令不同的是它这里是把rbd的大小转化成GB，然后再字符串拼接了一个“G”。这里我们就按照它这里的方法，组装了一个新的rbd命令，然后在CentOS上测试：
# rbd create cephrbd-test --size 5G
rbd: strict_strtoll: garbage at end of string. got: '5G'
果然，还是报错了，我们再使用该命令在ubuntu上测试：
# rbd create cephrbd-test --size 5G
在ubuntu上运行，没有报错。同一条命令，在不同的环境下结果不同。那么最大的可能就是rbd(ceph)的版本不一致了。在ubuntu下获取ceph版本。
# ceph version
ceph version 10.2.7
而CentOS上默认安装的ceph版本只是0.94.5(Hammer版)，而Ubuntu上默认安装的却是更高的10.2.7(jewel版本)。而0.94.5 ceph版本的rbd命令无法解析“G”，“M”等描述rbd大小的参数。这就是问题出现的原因。
解决方法
在CentOS上安装更新的Ceph版本(jewel或更新的版本)即可。
ps：后面的博客会介绍如何在CentOS上安装更新的Ceph版本。