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Today, a customer asked me how much disk storage a single VOS module can address. Here is my response.

The per-disk (actually, per LUN) storage limit for all V Series releases is 8.7 TB. A single VOS module supports a maximum of 256 LUNs. Therefore, the VOS software limit for total storage on a single module is 256 * 8.7T, which is 2.2 Petabytes (1 Petabyte equals 1000 Terabytes).

Now, consider the hardware limit. A single 2nd-generation ftScalable Storage array can support 72 drives. The largest drive that VOS currently supports is 300 GB. Therefore, the VOS hardware limit on a single module is 72 drives * 300 GB, which is 21.6 TB.  This calculation assumes NRAID at the ftScalable Storage level, with duplexing at the VOS level.

Thus, the current maximum hardware configuration can support about 1% of the maximum software configuration. That’s okay; we want the software limits to be a lot higher than the hardware limits, because the software limits are a lot harder to change.

Larger disk drives for 2nd-generation ftScalable Storage are on the way. It is likely that the next drive will have a capacity of 600GB. That drive will increase the hardware storage limit to 43TB.

In theory, VOS can also support additional RAID arrays, but we’ve never had a customer request it.

Note: Any POSIX code that uses huge LUNs must be built with either the _VOS_LARGE_INODE macro defined, or with one of the “large file” macros defined. This is because inode numbers on these huge LUNs require 64 bits of data. Our own layered products are built with this support enabled.

If you think your VOS-based application needs more storage than Stratus currently offers, please let us know your of your plans as far in advance as possible. We’ll work with you to craft a solution you can use.

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