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Yang, Tong
6182f91ba8
Reviewed-by: Hasko, Vladimir <vladimir.hasko@t-systems.com> Co-authored-by: Yang, Tong <yangtong2@huawei.com> Co-committed-by: Yang, Tong <yangtong2@huawei.com>
17 lines
2.3 KiB
HTML
17 lines
2.3 KiB
HTML
<a name="mrs_01_1701"></a><a name="mrs_01_1701"></a>
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<h1 class="topictitle1">Why Is the Storage Type of File Copies DISK When the Tiered Storage Policy Is LAZY_PERSIST?</h1>
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<div id="body1597735020143"><div class="section" id="mrs_01_1701__s0285524a0dcf4fbca4d0d61c952f4ac2"><h4 class="sectiontitle">Question</h4><p id="mrs_01_1701__a3828b8f75c0d40c498c76d78acfd2528">When the storage policy of the file is set to <strong id="mrs_01_1701__b9679464521624">LAZY_PERSIST</strong>, the storage type of the first replica should be <strong id="mrs_01_1701__b95391203421624">RAM_DISK</strong>, and the storage type of other replicas should be <strong id="mrs_01_1701__b173779388021624">DISK</strong>.</p>
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<p id="mrs_01_1701__ad3c200608bfe42ed905ee7ea0ef7561e">But why is the storage type of all copies shown as <strong id="mrs_01_1701__b195930953121624">DISK</strong> actually?</p>
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<div class="section" id="mrs_01_1701__s8b5f8d882f714696b2043d414361bda5"><h4 class="sectiontitle">Answer</h4><p id="mrs_01_1701__p33162912333">When a user writes into a file whose storage policy is <strong id="mrs_01_1701__b13235966721624">LAZY_PERSIST</strong>, three replicas are written one by one. The first replica is preferentially written into the DataNode where the client is located. The storage type of all replicas is <strong id="mrs_01_1701__b204200314021624">DISK</strong> in the following scenarios:</p>
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<ul id="mrs_01_1701__ul11988191918336"><li id="mrs_01_1701__li1998815191334">If the DataNode where the client is located does not have the RAM disk, the first replica is written into the disk of the DataNode where the client is located, and other replicas are written into the disks of other nodes.</li><li id="mrs_01_1701__li1994215409341">If the DataNode where the client is located has the RAM disk, and the value of <strong id="mrs_01_1701__b26255955721624">dfs.datanode.max.locked.memory</strong> is not specified or smaller than the value of <strong id="mrs_01_1701__b14369160921624">dfs.blocksize</strong>, the first replica is written into the disk of the DataNode where the client is located, and other replicas are written into the disks of other nodes.</li></ul>
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<div class="parentlink"><strong>Parent topic:</strong> <a href="mrs_01_1690.html">FAQ</a></div>
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