问：
我们公司主要从事邮件系统方面的业务，所以，这是一个关于邮件系统存储方面的一个问题。
邮件系统数据的特点就是小文件多，并且目录多，一部分数据访问频繁，读写删除操作也频繁（活跃用户的数据），还有一部分数据基本不访问（非活跃用户），很少有读写删除操作。
当一个有40万用户的邮件系统，那么存放邮件数据的存储目录下面会有非常多的目录和文件（一个用户一个HomeDir，用户HomeDir下面存放用户的邮件），HomeDir至少40万个，每个HomeDir下面可能有用户的自定义文件夹。HomeDir下面存放的用户邮件数量多少不等，最多的可能有800封以上的邮件，平均每人30封邮件左右。大部分邮件大小在5-100K左右，也存在一部分带有较大附件的邮件，大小在1M-10M之间。
以上是应用特点的简单介绍，针对这样的应用环境，应该如何选择存储设备？做什么样的RAID能达到最好的性能？如何部署备份系统？
像类似这样的应用应该还有很多，例如：flickr、bababian等等这样的网络相册应用，应该和邮件应用类似，都是小文件，访问频繁。也很想了解他们是如何选择和部署存储系统的。
目前，我们的存储在使用一段时间后，只能使用df命令来查看磁盘空间，使用du命令查看存储目录占用空间的时候将会用掉非常非常长的时间，这个时间是绝对不能忍受的长。
使用备份方法是每天用rsync，将发生变化的文件同步到另外一个存储空间上，我认为这不是一个较为理想的备份方式，希望能再进行改进。
在RAID方面，我们基本上选择的都是用RAID5，也有使用RAID10，但是感觉这两者在性能上没有什么明显区别。不知您是否有测试存储性能方法及测试模型，我也想对我们系统中这种环境下的存储进行测试和分析，希望能找到最佳的方案。
sansky答：
你所说的几个系统具有频繁访问、随机访问、文件数量大等特点，对服务器和存储的第一个要求是高IOPS。我个人对存储系统的建议如下：
1、存储设备的的cache IOPS最好不低于12W，磁盘IOPS不低于7w，也就是说必须是中端以上存储设备，低端设备的性能不足以满足系统要求；
2、建议采用全光纤存储设备；由于总容量不大，可以选择146GB磁盘。如果考虑到价格，也可以选择高性能的FC-SAS存储。
3、磁盘访问的性能将会是整个系统的瓶颈。建议存储设备的磁盘端口不少于4个，配置不少于3个JBOD,SBOD最好。磁盘总数量48块磁盘最好，建议少于32块。否则磁盘太少，存储设备的性能发挥不出来。
4、每个RAID组中的磁盘数量8-12个，优选RAID5。
5、40个homedir最好分散在4个以上的RAID组中，也就是不同的LUN中。无论是windows还是linux系统，当一个lun中的文件数量过大时，其文件系统检索和访问能力多会大幅度减小。homedir分散在多个lun中，减少每一个文件系统中的文件数量。
6、多个RAID组的优先级高于每个RAID组中的磁盘数量。
7、对于备份来讲，如果考虑价格，可以选择用备份软件。如果投资允许，可以考虑CDP软件。
一点拙见，仅供参考。
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