Constraints

Use of OMS is limited as follows.

**Table 1** OMS constraints
Item	Constraint
Objects with multiple versions	By default, OMS migrates only the latest version of objects in source buckets.
Storage class of destination buckets	The storage class of destination buckets can only be standard or infrequent access. You can change the storage class of destination buckets after the migration is complete.
Migration network	Only migrations over the Internet are supported.
Metadata migration	Only English characters, numbers, and hyphens (-) in metadata can be migrated. Chinese characters and symbols cannot be migrated, regardless of whether they are encoded. NOTE: Even if you choose not to migrate metadata, the Content-Type metadata will still be migrated to ensure that the migration runs properly.
Migration scope	A single migration task or migration task group can only migrate data of one bucket. If data of multiple buckets needs to be migrated, you need to create multiple tasks or task groups.
Migration speed	Generally, OMS can migrate 10 TB to 20 TB of data per day. However, the speed depends on the number and size of source objects and the transmission distance over the Internet between the source and destination buckets. You are advised to create a migration task to test the migration speed. The maximum migration speed is five times the average speed of a single task because up to five tasks can be executed concurrently in a region. If more concurrent migrations are required, contact OMS technical support.
Archived data	You need to restore archived data before the migration. Note that when there is archived data to be migrated, you need to: Create migration tasks after the restoration is complete. Configure a validity period for restored data based on the total amount of data to be migrated. This helps prevent migration failures because restored data becomes archived again during the migration. Pay your source cloud vendor for restoring archived data. To learn about the pricing details, contact your source cloud vendor.
Migration tasks	A maximum of five concurrent migration tasks are allowed for your account per region. NOTE: If your destination regions are CN North-Beijing1 and CN South-Guangzhou, you can run up to 10 migration tasks concurrently.
Migration tasks	A maximum of 5,000 migration tasks are allowed for your account per region within a 24-hour period.
Migration task groups	A maximum of five concurrent migration task groups are allowed for your account per region. NOTE: If your destination regions are CN North-Beijing1 and CN South-Guangzhou, you can run up to 10 migration task groups concurrently.
Synchronization tasks	Synchronization tasks share quotas with migration tasks and migration task groups, but enjoy a higher priority. A maximum of five concurrent synchronization tasks are allowed for your account per region.
Object list files	An object list file cannot exceed 1,024 MB. An object list file must be a .txt file, and its metadata Content-Type must be text/plain. An object list file must be in UTF-8 without BOM. Each line in an object list file can contain only one object name, and the object name must be URL encoded. Spaces are not allowed in each line in an object list file. Spaces may cause migration failures because they may be mistakenly identified as object names. The length of each line in an object list file cannot exceed 65,535 characters, or the migration will fail. The Content-Encoding metadata of an object list file must be left empty, or the migration will fail.
URL list files	A URL list file cannot exceed 1,024 MB. A URL list file must be a .txt file, and its metadata Content-Type must be text/plain. A URL list file must be in UTF-8 without BOM. Each line in a URL list file can contain only one URL and one destination object name. The length of each line in a URL list file cannot exceed 65,535 characters, or the migration will fail. The Content-Encoding metadata of a URL list file must be left empty, or the migration will fail. Spaces are not allowed in each line in a URL list file. Spaces may cause migration failures because they may be mistakenly identified as object names. In a URL list file, each line uses a tab character (\t) to separate the URL and destination object name. The format is [URL][Tab character][Destination object name]. Only the Chinese and special characters in the source and destination object names must be URL encoded. For example: http://xxx.xxx.xxx.xxx.com/doc/thefile2.txt doc/thefile2.txt http://xxx.xxx.xxx.xxx.com/the%20file.txt the%20file.txt http://xxx.xxx.xxx.xxx.com/the%20file2.txt the+file2.txt http://xxx.xxx.xxx.xxx.com/doc/thefile.txt doc/thefile.txt CAUTION: The URL encoding starts from the second character after the domain name in a line. Do not encode the protocol header, domain name, or slash before or after the domain name. Otherwise, the format verification will fail. In each line, use a tab character (Tab key on the keyboard) to separate the URL and the destination object name. Do not use spaces. In the preceding examples, after the files represented by the URLs are copied to the destination bucket, the objects are named doc/the file2.txt, the file.txt, the file2.txt, and doc/thefile.txt.
Failed object list files	A maximum of 100,000 failed objects can be recorded in a failed object list file. NOTE: If more than 100,000 objects fail to be migrated in a migration task, you are advised to rectify the fault based on the existing failed object list and perform the migration again.