Hey all, Just wanted to follow up with this for anyone experiencing the same issue.
First, I tried Qu's suggestion, of re-balancing to single, then re-balancing to RAID 6. I noticed when I completed the conversion to single, that a few drives didn't receive an identical amount of data. Balancing back to RAID 6 didn't totally work either. It definitely made it better, but I still had multiple stripes of varying widths. IIRC, I had one ~1.7TB stripe that went across all 7 drives, and then a conglomerate of stripes ranging from 2-5 drives wide, and sizes 30GB - 1TB. The majority of data was striped across all 7, but I was concerned that as I added data, I'd run into the same situation as before. This process took quite a long time, as you guys expected. About 11 days for RAID 6 -> Single -> Raid 6. Patience is a virtue with large arrays. Henk, for some reason I didn't receive the email suggesting using the -dstripes= filter until I was well into the conversion to single. Once I finished the RAID 6 -> Single -> RAID 6, I attempted your method. I'm happy to say that it worked, using -dstripes="1..6". This only took about 30 hours, as most of the data was striped correctly. When it finished, I was left with one RAID 6 profile, about ~2.50 TB striped across all 7 drives. As I understand, running a balance with the -dstripes="1..$drivecount-1" filter will force BTRFS to balance chunks that are not evenly striped across all drives. I will definitely have to keep this trick in mind in the future. A side note, I'm happy with how robust BTRFS is becoming. I had a sustained power outage while I wasn't home that resulted in an unclean shutdown in the middle of the balance. (I had preciously disconnected my UPS' USB connector to move the server to a different room and forgot to reconnect it. Doh!). When power was returned, it started right back up where it left off with no corruption or data loss. I have backups, but I wasn't looking forward to the idea of restoring 11 TB of data. Than you everyone for your help, and thank you for putting all this work into BTRFS. Your efforts are truly appreciated. Regards, Dan On Thu, Feb 18, 2016 at 8:36 PM, Qu Wenruo <quwen...@cn.fujitsu.com> wrote: > > > Henk Slager wrote on 2016/02/19 00:27 +0100: >> >> On Thu, Feb 18, 2016 at 3:03 AM, Qu Wenruo <quwen...@cn.fujitsu.com> >> wrote: >>> >>> >>> >>> Dan Blazejewski wrote on 2016/02/17 18:04 -0500: >>>> >>>> >>>> Hello, >>>> >>>> I upgraded my kernel to 4.4.2, and btrfs-progs to 4.4. I also added >>>> another 4TB disk and kicked off a full balance (currently 7x4TB >>>> RAID6). I'm interested to see what an additional drive will do to >>>> this. I'll also have to wait and see if a full system balance on a >>>> newer version of BTRFS tools does the trick or not. >>>> >>>> I also noticed that "btrfs device usage" shows multiple entries for >>>> Data, RAID 6 on some drives. Is this normal? Please note that /dev/sdh >>>> is the new disk, and I only just started the balance. >>>> >>>> # btrfs dev usage /mnt/data >>>> /dev/sda, ID: 5 >>>> Device size: 3.64TiB >>>> Data,RAID6: 1.43TiB >>>> Data,RAID6: 1.48TiB >>>> Data,RAID6: 320.00KiB >>>> Metadata,RAID6: 2.55GiB >>>> Metadata,RAID6: 1.50GiB >>>> System,RAID6: 16.00MiB >>>> Unallocated: 733.67GiB >>>> >>>> /dev/sdb, ID: 6 >>>> Device size: 3.64TiB >>>> Data,RAID6: 1.48TiB >>>> Data,RAID6: 320.00KiB >>>> Metadata,RAID6: 1.50GiB >>>> System,RAID6: 16.00MiB >>>> Unallocated: 2.15TiB >>>> >>>> /dev/sdc, ID: 7 >>>> Device size: 3.64TiB >>>> Data,RAID6: 1.43TiB >>>> Data,RAID6: 732.69GiB >>>> Data,RAID6: 1.48TiB >>>> Data,RAID6: 320.00KiB >>>> Metadata,RAID6: 2.55GiB >>>> Metadata,RAID6: 982.00MiB >>>> Metadata,RAID6: 1.50GiB >>>> System,RAID6: 16.00MiB >>>> Unallocated: 25.21MiB >>>> >>>> /dev/sdd, ID: 1 >>>> Device size: 3.64TiB >>>> Data,RAID6: 1.43TiB >>>> Data,RAID6: 732.69GiB >>>> Data,RAID6: 1.48TiB >>>> Data,RAID6: 320.00KiB >>>> Metadata,RAID6: 2.55GiB >>>> Metadata,RAID6: 982.00MiB >>>> Metadata,RAID6: 1.50GiB >>>> System,RAID6: 16.00MiB >>>> Unallocated: 25.21MiB >>>> >>>> /dev/sdf, ID: 3 >>>> Device size: 3.64TiB >>>> Data,RAID6: 1.43TiB >>>> Data,RAID6: 732.69GiB >>>> Data,RAID6: 1.48TiB >>>> Data,RAID6: 320.00KiB >>>> Metadata,RAID6: 2.55GiB >>>> Metadata,RAID6: 982.00MiB >>>> Metadata,RAID6: 1.50GiB >>>> System,RAID6: 16.00MiB >>>> Unallocated: 25.21MiB >>>> >>>> /dev/sdg, ID: 2 >>>> Device size: 3.64TiB >>>> Data,RAID6: 1.43TiB >>>> Data,RAID6: 732.69GiB >>>> Data,RAID6: 1.48TiB >>>> Data,RAID6: 320.00KiB >>>> Metadata,RAID6: 2.55GiB >>>> Metadata,RAID6: 982.00MiB >>>> Metadata,RAID6: 1.50GiB >>>> System,RAID6: 16.00MiB >>>> Unallocated: 25.21MiB >>>> >>>> /dev/sdh, ID: 8 >>>> Device size: 3.64TiB >>>> Data,RAID6: 320.00KiB >>>> Unallocated: 3.64TiB >>>> >>> >>> Not sure how that multiple chunk type shows up. >>> Maybe all these shown RAID6 has different number of stripes? >> >> >> Indeed, its 4 different sets of stripe-widths, i.e. how many drives is >> striped accross. Someone has suggested to indicate this in the output >> of btrfs de us comand some time ago. >> >> The fs has only RAID6 profile and I am not fully sure if the >> 'Unallocated' numbers are correct (on RAID10 they are 2x too high >> with unpatched v4.4 progs), but anyhow the lower devid's are way too >> full. >> >> From the size, one can derive how many devices (or stipe-width): >> 732.69GiB 4, 1.43TiB 5, 1.48TiB 6, 320.00KiB 7 >> >>>> Qu, in regards to your question, I ran RAID 1 on multiple disks of >>>> different sizes. I believe I had a mix of 2x4TB, 1x2TB, and 1x3TB >>>> drive. I replaced the 2TB drive first with a 4TB, and balanced it. >>>> Later on, I replaced the 3TB drive with another 4TB, and balanced, >>>> yielding an array of 4x4TB RAID1. A little while later, I wound up >>>> sticking a fifth 4TB drive in, and converting to RAID6. The sixth 4TB >>>> drive was added some time after that. The seventh was added just a few >>>> minutes ago. >>> >>> >>> >>> Personally speaking, I just came up to one method to balance all these >>> disks, and in fact you don't need to add a disk. >>> >>> 1) Balance all data chunk to single profile >>> 2) Balance all metadata chunk to single or RAID1 profile >>> 3) Balance all data chunk back to RAID6 profile >>> 4) Balance all metadata chunk back to RAID6 profile >>> System chunk is so small that normally you don't need to bother. >>> >>> The trick is, as single is the most flex chunk type, only needs one disk >>> with unallocated space. >>> And btrfs chunk allocater will allocate chunk to device with most >>> unallocated space. >>> >>> So after 1) and 2) you should found that chunk allocation is almost >>> perfectly balanced across all devices, as long as they are in same size. >>> >>> Now you have a balance base layout for RAID6 allocation. Should make >>> things >>> go quite smooth and result a balanced RAID6 chunk layout. >> >> >> This is a good trick to get out of 'the RAID6 full' situation. I have >> done some RAID5 tests on 100G VM disks with kernel/tools 4.5-rcX/v4.4, >> and various balancing starts, cancels, profile converts etc, worked >> surprisingly well, compared to my experience a year back with RAID5 >> (hitting bugs, crashes). >> >> A RAID6 full balance with this setup might be very slow, even if the >> fs would be not so full. The VMs I use are on a mixed SSD/HDD >> (bcache'd) array so balancing within the last GB(s), so almost no >> workspace, still makes progress. But on HDD only, things can take very >> long. The 'Unallocated' space on devid 1 should be at least a few GiB, >> otherwise rebalancing will be very slow or just not work. > > > That's true the rebalance of all chunks will be quite slow. > I just hope OP won't encounter super slow > > BTW, the 'unallocated' space can on any device, as btrfs will choose devices > by the order of unallocated space, to alloc new chunk. > In the case of OP, balance itself should continue without much porblem as > several devices have a lot of unallocated space. > >> >> The way from RAID6 -> single/RAID1 -> RAID6 might also be more >> acceptable w.r.t. speed in total. Just watch progress I would say. >> Maybe its not needed to do a full convert, just make sure you will >> have enough workspace before starting a convert from single/RAID1 to >> RAID6 again. >> >> With v4.4 tools, you can do filtered balance based on stripe-width, so >> it avoids complete balance again of block groups that are already >> allocated across the right amount of devices. >> >> In this case, avoiding the re-balance of the '320.00KiB group' (in the >> means time could be much larger) you could do this: >> btrfs balance start -v -dstripes=1..6 /mnt/data > > > Super brilliant idea!!! > > I didn't realize that's the silver bullet for such use case. > > BTW, can stripes option be used with convert? > IMHO we still need to use single as a temporary state for those not fully > allocated RAID6 chunks. > Or we won't be able to alloc new RAID6 chunk with full stripes. > > Thanks, > Qu > > >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in >> the body of a message to majord...@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> >> > > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
