1. 载体崩溃
当出现硬件问题或文件系统出错，特别是硬盘损坏了，就没法保护数据安全了。另外，不同品牌的硬件和软件具有不同的持久保证的。
总而言之，如果硬件或文件系统破坏了数据，MongoDB是无法保护数据的，这已经属于底层存储的事情了。可以使用复制来避免这个问题，其实就是单点问题了。文章源自运维生存时间-https://www.ttlsa.com/mongodb/mongodb-durability-3/
2. 检查损坏
validate命令用来检测一个集合的损坏，如：文章源自运维生存时间-https://www.ttlsa.com/mongodb/mongodb-durability-3/
> db.posts.validate({full:true})
{
"ns" : "ttlsa_com.posts",
"firstExtent" : "1:1036000 ns:ttlsa_com.posts",
"lastExtent" : "4:2000 ns:ttlsa_com.posts",
"extentCount" : 14,
"extents" : [
{
"loc" : "1:1036000",
"xnext" : "1:104e000",
"xprev" : "null",
"nsdiag" : "ttlsa_com.posts",
"size" : 61440,
"firstRecord" : "1:1037c30",
"lastRecord" : "1:103e4f0"
},
{
"loc" : "1:104e000",
"xnext" : "1:108a000",
"xprev" : "1:1036000",
"nsdiag" : "ttlsa_com.posts",
"size" : 245760,
"firstRecord" : "1:104e0b0",
"lastRecord" : "1:10556b0"
},
{
"loc" : "1:108a000",
"xnext" : "1:117a000",
"xprev" : "1:104e000",
"nsdiag" : "ttlsa_com.posts",
"size" : 983040,
"firstRecord" : "1:108a0b0",
"lastRecord" : "1:109a9b0"
},
{
"loc" : "1:117a000",
"xnext" : "1:155e000",
"xprev" : "1:108a000",
"nsdiag" : "ttlsa_com.posts",
"size" : 3932160,
"firstRecord" : "1:117a0b0",
"lastRecord" : "1:13739f0"
},
{
"loc" : "1:155e000",
"xnext" : "1:24ee000",
"xprev" : "1:117a000",
"nsdiag" : "ttlsa_com.posts",
"size" : 15728640,
"firstRecord" : "1:155e0b0",
"lastRecord" : "1:1bbe4f0"
},
{
"loc" : "1:24ee000",
"xnext" : "1:392e000",
"xprev" : "1:155e000",
"nsdiag" : "ttlsa_com.posts",
"size" : 21233664,
"firstRecord" : "1:24ee8b0",
"lastRecord" : "1:2b485b0"
},
{
"loc" : "1:392e000",
"xnext" : "1:56c5000",
"xprev" : "1:24ee000",
"nsdiag" : "ttlsa_com.posts",
"size" : 28667904,
"firstRecord" : "1:392e0b0",
"lastRecord" : "1:450dd30"
},
{
"loc" : "1:56c5000",
"xnext" : "2:2000",
"xprev" : "1:392e000",
"nsdiag" : "ttlsa_com.posts",
"size" : 38703104,
"firstRecord" : "1:56c50b0",
"lastRecord" : "1:617c0b0"
},
{
"loc" : "2:2000",
"xnext" : "2:3ad7000",
"xprev" : "1:56c5000",
"nsdiag" : "ttlsa_com.posts",
"size" : 52252672,
"firstRecord" : "2:20b0",
"lastRecord" : "2:188ac30"
},
{
"loc" : "2:3ad7000",
"xnext" : "2:7e1d000",
"xprev" : "2:2000",
"nsdiag" : "ttlsa_com.posts",
"size" : 70541312,
"firstRecord" : "2:3ad7470",
"lastRecord" : "2:66b8af0"
},
{
"loc" : "2:7e1d000",
"xnext" : "3:2000",
"xprev" : "2:3ad7000",
"nsdiag" : "ttlsa_com.posts",
"size" : 95232000,
"firstRecord" : "2:7e1d0b0",
"lastRecord" : "2:be8a2b0"
},
{
"loc" : "3:2000",
"xnext" : "3:dd21000",
"xprev" : "2:7e1d000",
"nsdiag" : "ttlsa_com.posts",
"size" : 128565248,
"firstRecord" : "3:20b0",
"lastRecord" : "3:63eb670"
},
{
"loc" : "3:dd21000",
"xnext" : "4:2000",
"xprev" : "3:2000",
"nsdiag" : "ttlsa_com.posts",
"size" : 173563904,
"firstRecord" : "3:dd210b0",
"lastRecord" : "3:12fccc30"
},
{
"loc" : "4:2000",
"xnext" : "null",
"xprev" : "3:dd21000",
"nsdiag" : "ttlsa_com.posts",
"size" : 234311680,
"firstRecord" : "4:20b0",
"lastRecord" : "4:7bec3b0"
}
],
"datasize" : 614217440,
"nrecords" : 305603,
"lastExtentSize" : 234311680,
"padding" : 1.0000000000221079,
"firstExtentDetails" : {
"loc" : "1:1036000",
"xnext" : "1:104e000",
"xprev" : "null",
"nsdiag" : "ttlsa_com.posts",
"size" : 61440,
"firstRecord" : "1:1037c30",
"lastRecord" : "1:103e4f0"
},
"lastExtentDetails" : {
"loc" : "4:2000",
"xnext" : "null",
"xprev" : "3:dd21000",
"nsdiag" : "ttlsa_com.posts",
"size" : 234311680,
"firstRecord" : "4:20b0",
"lastRecord" : "4:7bec3b0"
},
"objectsFound" : 305603,
"invalidObjects" : 0,
"bytesWithHeaders" : 619107088,
"bytesWithoutHeaders" : 614217440,
"deletedCount" : 125358,
"deletedSize" : 244912976,
"nIndexes" : 9,
"keysPerIndex" : {
"ttlsa_com.posts.$_id_" : 305603,
"ttlsa_com.posts.$index_doctorSn" : 305603,
"ttlsa_com.posts.$index_doctorUid" : 305603,
"ttlsa_com.posts.$index_hosDeptId" : 305603,
"ttlsa_com.posts.$index_hospitalId" : 305603,
"ttlsa_com.posts.$doctorNumberList_1_doctorOrderId_-1" : 305924,
"ttlsa_com.posts.$cityId_1_displayStatus_1" : 305603,
"ttlsa_com.posts.$standardDeptId_1_displayStatus_1" : 305603,
"ttlsa_com.posts.$doctorCode_1" : 305603
},
"valid" : true,
"errors" : [ ],
"ok" : 1
}
在上面输出底部，有个"valid" : true 说明没有损坏，如果不是，会找到一些损坏的细节。大部分输出是描述集合内部的结构，对于调试不是特别有用的。文章源自运维生存时间-https://www.ttlsa.com/mongodb/mongodb-durability-3/
只能检测集合，不能检测索引。文章源自运维生存时间-https://www.ttlsa.com/mongodb/mongodb-durability-3/
如果出现无效的BSONbj，通常就是损坏了。最糟糕的是出现pdfile，pdfile基本上是mongodb的数据存储核心，几乎可以判断数据文件已经损坏了。文章源自运维生存时间-https://www.ttlsa.com/mongodb/mongodb-durability-3/
如果出现损坏，会看到下面的日志信息：文章源自运维生存时间-https://www.ttlsa.com/mongodb/mongodb-durability-3/
Tue Dec 20 01:12:09 [initandlisten] Assertion: 10334:
Invalid BSONObj size: 285213831 (0x87040011)
first element: _id: ObjectId('4e5efa454b4ae20fa6000013')文章源自运维生存时间-https://www.ttlsa.com/mongodb/mongodb-durability-3/
如果第一个元素显示的是垃圾，不需要做什么。如果第一个元素是可见的，可以移除损坏的文档。如：文章源自运维生存时间-https://www.ttlsa.com/mongodb/mongodb-durability-3/
> db.remove({_id: ObjectId('4e5efa454b4ae20fa6000013')})文章源自运维生存时间-https://www.ttlsa.com/mongodb/mongodb-durability-3/
如果损坏并不局限于该文档，这种技术可能无法工作，你仍然需要进行修复。文章源自运维生存时间-https://www.ttlsa.com/mongodb/mongodb-durability-3/
3. 复制的持久性
复制集一个写可被回滚，直到它被写入到一个大多数的集合中。文章源自运维生存时间-https://www.ttlsa.com/mongodb/mongodb-durability-3/
> db.runCommand({"getLastError" : 1, "j" : true, "w" : "majority"})文章源自运维生存时间-https://www.ttlsa.com/mongodb/mongodb-durability-3/
只能保证primary写入已经持久化，secondary未必持久化。文章源自运维生存时间-https://www.ttlsa.com/mongodb/mongodb-durability-3/ 文章源自运维生存时间-https://www.ttlsa.com/mongodb/mongodb-durability-3/
来自外部的引用