On Saturday February 18, hardyjm@xxxxxxxxxxx wrote: > I'm running 2.6.14.6 with CONFIG_LBD yes, with access to some pretty > large AoE block devices. When I try to create a RAID1 between a couple > of block devices larger than 4TB, mdadm complains with: > > mdadm: devices too large for RAID level 1 > > As long as I back the size down to 4TB or less, it will work. This is a > bit confusing, because I searched through the archives and did not find > much mention of max RAID size limits except for this about a 2TB maximum > size for RAID5 component devices: > > http://marc.theaimsgroup.com/?l=linux-raid&m=112782802028969&w=2 > > Mdadm (1.11.0 and newer) does this maximum size check for anything > higher than RAID level 0, so I would assume RAID1 and RAID5 would be the > same. > > Apologies if this is obvious but: what is the current actual size limit > for component devices in RAID levels greater than zero? The amount of each component drive this is actually in use is stored - in the default metadata - in a 32bit number as kilobytes. This sets a limit of 4TB. The version-1 metadata format has a 64bit field. If you use mdadm 2.3, it will automatically select version-1 metadata if you choose a size larger than 2TB (I think). You might also need a very recent (16-rc) kernel for v.large raid1 to work. There were bugs related to this usage pattern that were fixed only recently. To avoid resyncing >4TB, use of a write-intent-bitmap is strongly recommended. NeilBrown - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
