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| <h1>Ozone Manager</h1> |
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| <p>Ozone Manager(OM)管理 Ozone 的命名空间。</p> |
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| <p>当向 Ozone 写入数据时,你需要向 OM 请求一个块,OM 会返回一个块并记录下相关信息。当你想要读取那个文件时,你也需要先通过 OM 获取那个块的地址。</p> |
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| <p>OM 允许用户在卷和桶下管理键,卷和桶都是命名空间的一部分,也由 OM 管理。</p> |
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| <p>每个卷都是 OM 下的一个独立命名空间的根,这一点和 HDFS 不同,HDFS 提供的是单个根目录的文件系统。</p> |
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| <p>与 HDFS 中单根的树状结构相比,Ozone 的命名空间是卷的集合,或者可以看作是个森林,因此可以非常容易地部署多个 OM 来进行扩展。</p> |
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| <h2 id="ozone-manager-元数据">Ozone Manager 元数据</h2> |
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| <p>OM 维护了卷、桶和键的列表。它为每个用户维护卷的列表,为每个卷维护桶的列表,为每个桶维护键的列表。</p> |
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| <p>OM 使用 Apache Ratis(Raft 协议的一种实现)来复制 OM 的状态,这为 Ozone 提供了高可用性保证。</p> |
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| <h2 id="ozone-manager-和-storage-container-manager">Ozone Manager 和 Storage Container Manager</h2> |
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| <p>为了方便理解 OM 和 SCM 之间的关系,我们来看看写入键和读取键的过程。</p> |
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| <h3 id="写入键">写入键</h3> |
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| <ul> |
| <li><p>为了向 Ozone 中的某个卷下的某个桶的某个键写入数据,用户需要先向 OM 发起写请求,OM 会判断该用户是否有权限写入该键,如果权限许可,OM 分配一个块用于 Ozone 客户端数据写入。</p></li> |
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| <li><p>OM 通过 SCM 请求分配一个块(SCM 是数据节点的管理者),SCM 选择三个数据节点,分配新块并向 OM 返回块标识。</p></li> |
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| <li><p>OM 在自己的元数据中记录下块的信息,然后将块和块 token(带有向该块写数据的授权)返回给用户。</p></li> |
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| <li><p>用户使用块 token 证明自己有权限向该块写入数据,并向对应的数据节点写入数据。</p></li> |
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| <li><p>数据写入完成后,用户会更新该块在 OM 中的信息。</p></li> |
| </ul> |
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| <h3 id="读取键">读取键</h3> |
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| <ul> |
| <li><p>键读取相对比较简单,用户首先向 OM 请求该键的块列表。</p></li> |
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| <li><p>OM 返回块列表以及对应的块 token。</p></li> |
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| <li><p>用户连接数据节点,出示块 token,然后读取键数据。</p></li> |
| </ul> |
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