Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
Hello all, I'd need to use drbd on a lot of small partitions. One bit of Metatdata represents 4096 bit as far as I understood. So 128 MB represent up to 4TB. I have limited hardware and would like not to waste space. Since I only need to have e.g. a partition with 256MB usable size, I guess (2^8 * 2^20) / 2^12 bit = 2^16 bit = 8192 B would be enough. For sure that is only the space for the bitmap and needs some additional space for the rest of the MD. As far as I understood the following definitions in drbd/drbd_int.h: - #define MD_GC_OFFSET 0 - #define MD_AL_OFFSET 8 // 8 Sectors after start of meta area - #define MD_AL_MAX_SIZE 64 // = 32 kb LOG ~ 3776 extents ~ 14 GB Storage - #define MD_BM_OFFSET (MD_AL_OFFSET + MD_AL_MAX_SIZE) //Allows up to about 3.8TB the rest of the MD would be (please correct me if I'm wrong): - GC (means ?): 8 Sectors = 8*4096bit = 4KB - AL ("Action Log"): 64 Sectors = 64*4096bit = 32KB so the MD would be 36KB plus the size of the bitmap? I did some tests and adjusted the #define MD_RESERVED_SIZE ( 128LU * (1<<10) ) // 128 MB ( in units of kb ) line in drbd/drbd_int.h to e.g. (still more than enough): #define MD_RESERVED_SIZE ( 1LU * (1<<10) ) // 1 MB ( in units of kb ) and experienced no unexpected behaviour while playing around with a newly created partition. So my question is - has anyone tried that before? Does anyone see any problems when I use that in an working environment? Do I have major bugs in my calculations? I tried to analyze the code to find something that forbids it but I didn't find anything. I found a comment that I should use version 0.6 if I want to have it for small devices but if it works like that I could use 0.7 until 0.8(with dynamic BM size?) will be released. Some facts: - I used drbd 0.7.16 for the tests. - All my partitions will have the same size which will *never* be altered. - When I tried with MD below the calculated size I experienced problems. (writes to the MD "killed" the filesystem since parts were overwritten) Thanks for all comments Martin -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.linbit.com/pipermail/drbd-user/attachments/20060313/7236f076/attachment.htm>