Re: [RFC] How to enable btrfs reserve block space from specific device?
On Wed, Mar 27, 2013 at 09:45:59AM +0800, Zhi Yong Wu wrote: HI, When i work on btrfs hot relocation feature, i hit one question about block reservation. btrfs hot relocation need to reserve block space from specific devices such as SSD, but current btrfs reserving code doesn't differentiate if block space is reserved from SSD or HDD. In order to make btrfs support this, I thought that we can introduce one new block group or flag, but this will maybe make large impact on current existing other functions. For this, does any guy have some better idea? thanks. Hi, Sorry for the late reply. I have a lot on my plate right now, so I haven't looked at your WIP code. However, based on my knowledge, I can tell you that block reservation problem is completely orthogonal to the way you choose to handle hot data storage. A separate block group is one way to do it, and probably the easiest one. Block groups - chunks is a 1:1 mapping, so, for now, it might make sense to have one giant block group spanning over the entire hot data device. OTOH, IIRC the original implementation from IBM just used the rotation flag to detect hot data devices. You have a lot of choices here, but, if you are planning on implementing mirrored/striped hot data devices in future, I'd definitely go with block groups, since that'll give you some of the infrastructure for that for free. Thanks, Ilya -- 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
Re: [RFC] How to enable btrfs reserve block space from specific device?
On Wed, Mar 27, 2013 at 7:34 PM, Ilya Dryomov idryo...@gmail.com wrote: On Wed, Mar 27, 2013 at 09:45:59AM +0800, Zhi Yong Wu wrote: HI, When i work on btrfs hot relocation feature, i hit one question about block reservation. btrfs hot relocation need to reserve block space from specific devices such as SSD, but current btrfs reserving code doesn't differentiate if block space is reserved from SSD or HDD. In order to make btrfs support this, I thought that we can introduce one new block group or flag, but this will maybe make large impact on current existing other functions. For this, does any guy have some better idea? thanks. Hi, Sorry for the late reply. I have a lot on my plate right now, so I No matter, thanks for you reply. it is definitely very helpful to me, thanks. haven't looked at your WIP code. However, based on my knowledge, I can tell you that block reservation problem is completely orthogonal to the way you choose to handle hot data storage. A separate block group is one way to do it, and probably the easiest one. Block groups - chunks is a 1:1 mapping, so, for now, it might make sense to have one giant Yes, bg:chunks is 1:1 mapping. block group spanning over the entire hot data device. OTOH, IIRC the If so,when hot relocation is enabled, will the other btrfs functions reserve block space only from HDD? In this case, will SSD seem to be only used as one cache? original implementation from IBM just used the rotation flag to detect yes, it determine if one device is SSD by one flag in request queue of that device. hot data devices. You have a lot of choices here, but, if you are planning on implementing mirrored/striped hot data devices in future, This is maybe next item, i will put it and meta relocation support in my TODO list. I'd definitely go with block groups, since that'll give you some of the infrastructure for that for free. Thanks, Ilya -- Regards, Zhi Yong Wu -- 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
[RFC] How to enable btrfs reserve block space from specific device?
HI, When i work on btrfs hot relocation feature, i hit one question about block reservation. btrfs hot relocation need to reserve block space from specific devices such as SSD, but current btrfs reserving code doesn't differentiate if block space is reserved from SSD or HDD. In order to make btrfs support this, I thought that we can introduce one new block group or flag, but this will maybe make large impact on current existing other functions. For this, does any guy have some better idea? thanks. -- Regards, Zhi Yong Wu -- 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
