Re: Can btrfs silently repair read-error in raid1
On 08-05-2012 18:47, Hubert Kario wrote: On Tuesday 08 of May 2012 04:45:51 cwillu wrote: On Tue, May 8, 2012 at 1:36 AM, Fajar A. Nugraha wrote: On Tue, May 8, 2012 at 2:13 PM, Clemens Eisserer wrote: Hi, I have a quite unreliable SSD here which develops some bad blocks from time to time which result in read-errors. Once the block is written to again, its remapped internally and everything is fine again for that block. Would it be possible to create 2 btrfs partitions on that drive and use it in RAID1 - with btrfs silently repairing read-errors when they occur? Would it require special settings, to not fallback to read-only mode when a read-error occurs? The problem would be how the SSD (and linux) behaves when it encounters bad blocks (not bad disks, which is easier). If it does "oh, I can't read this block. I just return an error immediately", then it's good. However, in most situation, it would be like "hmmm, I can't read this block, let me retry that again. What? still error? then lets retry it again, and again.", which could take several minutes for a single bad block. And during that time linux (the kernel) would do something like "hey, the disk is not responding. Why don't we try some stuff? Let's try resetting the link. If it doesn't work, try downgrading the link speed". In short, if you KNOW the SSD is already showing signs of bad blocks, better just throw it away. The excessive number of retries (basically, the kernel repeating the work the drive already attempted) is being addressed in the block layer. "[PATCH] libata-eh don't waste time retrying media errors (v3)", I believe this is queued for 3.5 I just hope they don't remove retries completely, I've seen the second or third try return correct data on multiple disks from different vendors. (Which allowed me to use dd to write the data back to force relocation) But yes, Linux is a bit too overzelous with regards to retries... Regards, I hope they do. If you wish, you can force the retry, just trying your command again. This decision should happen in a higher level. -- 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: Can btrfs silently repair read-error in raid1
On 08/05/12 17:13, Clemens Eisserer wrote: > Would it be possible to create 2 btrfs partitions on that drive and > use it in RAID1 - with btrfs silently repairing read-errors when they > occur? You can, I tried that in 2009: http://www.csamuel.org/2009/01/04/btrfs-raid1-benchmark-on-dell-e4200-with-128gb-ssd But as Chris Mason pointed out on list at that time, it doesn't necessarily mean you're any safer due to the way that FTL's work: http://permalink.gmane.org/gmane.comp.file-systems.btrfs/2575 cheers, Chris -- Chris Samuel : http://www.csamuel.org/ : Melbourne, VIC -- 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: Can btrfs silently repair read-error in raid1
On Tuesday 08 of May 2012 04:45:51 cwillu wrote: > On Tue, May 8, 2012 at 1:36 AM, Fajar A. Nugraha wrote: > > On Tue, May 8, 2012 at 2:13 PM, Clemens Eisserer wrote: > >> Hi, > >> > >> I have a quite unreliable SSD here which develops some bad blocks from > >> time to time which result in read-errors. > >> Once the block is written to again, its remapped internally and > >> everything is fine again for that block. > >> > >> Would it be possible to create 2 btrfs partitions on that drive and > >> use it in RAID1 - with btrfs silently repairing read-errors when they > >> occur? > >> Would it require special settings, to not fallback to read-only mode > >> when a read-error occurs? > > > > The problem would be how the SSD (and linux) behaves when it > > encounters bad blocks (not bad disks, which is easier). > > > > If it does "oh, I can't read this block. I just return an error > > immediately", then it's good. > > > > However, in most situation, it would be like "hmmm, I can't read this > > block, let me retry that again. What? still error? then lets retry it > > again, and again.", which could take several minutes for a single bad > > block. And during that time linux (the kernel) would do something like > > "hey, the disk is not responding. Why don't we try some stuff? Let's > > try resetting the link. If it doesn't work, try downgrading the link > > speed". > > > > In short, if you KNOW the SSD is already showing signs of bad blocks, > > better just throw it away. > > The excessive number of retries (basically, the kernel repeating the > work the drive already attempted) is being addressed in the block > layer. > > "[PATCH] libata-eh don't waste time retrying media errors (v3)", I > believe this is queued for 3.5 I just hope they don't remove retries completely, I've seen the second or third try return correct data on multiple disks from different vendors. (Which allowed me to use dd to write the data back to force relocation) But yes, Linux is a bit too overzelous with regards to retries... Regards, -- Hubert Kario QBS - Quality Business Software 02-656 Warszawa, ul. Ksawerów 30/85 tel. +48 (22) 646-61-51, 646-74-24 www.qbs.com.pl -- 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: Can btrfs silently repair read-error in raid1
On Tue, May 8, 2012 at 1:36 AM, Fajar A. Nugraha wrote: > On Tue, May 8, 2012 at 2:13 PM, Clemens Eisserer wrote: >> Hi, >> >> I have a quite unreliable SSD here which develops some bad blocks from >> time to time which result in read-errors. >> Once the block is written to again, its remapped internally and >> everything is fine again for that block. >> >> Would it be possible to create 2 btrfs partitions on that drive and >> use it in RAID1 - with btrfs silently repairing read-errors when they >> occur? >> Would it require special settings, to not fallback to read-only mode >> when a read-error occurs? > > The problem would be how the SSD (and linux) behaves when it > encounters bad blocks (not bad disks, which is easier). > > If it does "oh, I can't read this block. I just return an error > immediately", then it's good. > > However, in most situation, it would be like "hmmm, I can't read this > block, let me retry that again. What? still error? then lets retry it > again, and again.", which could take several minutes for a single bad > block. And during that time linux (the kernel) would do something like > "hey, the disk is not responding. Why don't we try some stuff? Let's > try resetting the link. If it doesn't work, try downgrading the link > speed". > > In short, if you KNOW the SSD is already showing signs of bad blocks, > better just throw it away. The excessive number of retries (basically, the kernel repeating the work the drive already attempted) is being addressed in the block layer. "[PATCH] libata-eh don't waste time retrying media errors (v3)", I believe this is queued for 3.5 -- 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: Can btrfs silently repair read-error in raid1
On Tue, May 8, 2012 at 2:13 PM, Clemens Eisserer wrote: > Hi, > > I have a quite unreliable SSD here which develops some bad blocks from > time to time which result in read-errors. > Once the block is written to again, its remapped internally and > everything is fine again for that block. > > Would it be possible to create 2 btrfs partitions on that drive and > use it in RAID1 - with btrfs silently repairing read-errors when they > occur? > Would it require special settings, to not fallback to read-only mode > when a read-error occurs? The problem would be how the SSD (and linux) behaves when it encounters bad blocks (not bad disks, which is easier). If it does "oh, I can't read this block. I just return an error immediately", then it's good. However, in most situation, it would be like "hmmm, I can't read this block, let me retry that again. What? still error? then lets retry it again, and again.", which could take several minutes for a single bad block. And during that time linux (the kernel) would do something like "hey, the disk is not responding. Why don't we try some stuff? Let's try resetting the link. If it doesn't work, try downgrading the link speed". In short, if you KNOW the SSD is already showing signs of bad blocks, better just throw it away. -- Fajar -- 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: Can btrfs silently repair read-error in raid1
On Tue, May 08, 2012 at 09:13 (+0200), Clemens Eisserer wrote: > Would it be possible to create 2 btrfs partitions on that drive and > use it in RAID1 - with btrfs silently repairing read-errors when they > occur? > Would it require special settings, to not fallback to read-only mode > when a read-error occurs? No special settings required, that's exactly what btrfs is doing by default. Though, it's not completely silent: it will tell you in your kernel log about the repair it did. -Jan -- 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
Can btrfs silently repair read-error in raid1
Hi, I have a quite unreliable SSD here which develops some bad blocks from time to time which result in read-errors. Once the block is written to again, its remapped internally and everything is fine again for that block. Would it be possible to create 2 btrfs partitions on that drive and use it in RAID1 - with btrfs silently repairing read-errors when they occur? Would it require special settings, to not fallback to read-only mode when a read-error occurs? Thank you in advance, Clemens -- 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
