Showing posts from March, 2012

Storage Spaces

Based on this MS blog post, once you lost a storage space configuration, it is just lost.

At the moment, there is a significant difficulty recovering JBODs automatically. What the Storage Spaces subsystem does is, in effect, creation of JBODs of 256MB blocks. So in the end you can have just a plain JBOD, RAID 1 over JBODs, or RAID 5 over JBOD configuration. The capability to put 256MB blocks back into the pool and then use them again as needed, probably for another volume, leads to fragmentation on the pool level. That is, the volume itself gets fragmented, and obvously alignment gets out of window.

This means no RAID recovery on Storage Spaces unless some significant breakthroughs are made. Even simple volumes will not be recoverable if they got fragmented.

ReFS, first impression


1. Has more disk space overhead, both per-filesystem and per-file, than probably any other filesystem in existence.

2. Does not have a CHKDSK, which they might have to correct later.

3. Looks like it cannot achieve 32767 Unicode characters in file name, stopping short by ten characters or so; however we still did not test that.

4. Has several single points of failure, regardless of what they might say.

RAID levels explained

Once again an explanation of RAID levels, this time a fun one

and by the way, drop me a note if anyone knows the author?

Hot swap and hot spare revisited.

There are three levels of hot-something hardware repair capability in a storage system
cold swaphot swaphot spare
differing on two properties
if a downtime is required to perform the repairif a human intervention is required
Hence, the levels break down as follows:
Cold swap: both downtime and human intervention requiredHot swap: human intervention is required but no downtimeHot spare: no downtime and no human intervention

The price of the system increases with the level of hotness, while the maintenance cost decreases. In certain applications, where the maintenance cost is high, it is cheaper to put in enough "hot spare" parts for the entire useful life of the system than to use a hot-swap and human intervention. While an unmanned spacecraft is the extreme example of the high-cost maintenance, we will probably see maintenance-free end-user systems soon after hard drive production finally comes back to proper rates.