One of the first decisions you will need to make when tuning your environment for Cloud Storage I/O is what page size you will use to perform writes to your Cloud Storage Provider (CSP). This is one of the configuration parameters you will enter when configuring a new volume in CloudArray.
Page sizing is an important consideration, and represents the smallest unit of data that will be sent to your CSP from your CloudArray appliance, or read back when needed. Choose a size that is too small and you may have to do a lot more I/Os if you need to move a lot of data in bulk. Choose a size that’s too big and you will move more data than you need to.
For example, if your application needs to read a lot of small chunks of data that don’t already reside in your CloudArray cache, then CloudArray will have to issue read requests to the CSP for each of those chunks. If each chunk was 64K in length, and they weren’t contiguous, then CloudArray might have to issue 4 separate read requests for that data. If the data were contiguous, then only 1 read request would need to be made.
Larger Page Sizes will result in more data being read than is needed for the current operation, but it may help performance if that data is needed at any point while it is still in cache. In CloudArray, you can choose variable page sizes from 128 KB (default) all the way to 2 MB. 512 KB is the recommended value for backups and in cases where there is a lot of sequential I/O.
If you do a lot of random small block I/O, you should choose the smaller default page size. This will prevent having to move a lot of empty data between your CSP and the CloudArray appliance. A large page size here will cause slower overall performance since a lot more pages will have to be written to accommodate the data requirements. Likewise, if you are doing backups, you will want the 512 KB (or larger) page size. This will result in fewer overall writes compared to a smaller block size and performance will increase.
This can have an impact in your cost model as well, but nowhere nearly as much as some vendors selling file system-based appliances would have you believe. Some CSP’s will charge a small per transaction fee for each read or write request you make. For Amazon S3 for example, the charge is $0.00001 per write transaction. And so for a 1TB backup, that amounts to 8,388,608 x 128KB transactions, or $83. If you used a 512KB page size, that would amount to 2,097,152 write transactions, or $20 for the write transaction costs. Reads are cheaper by an order of ten. That’s a far cry from the $1K+ figure for a 100GB write that another vendor would cost you.
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