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Jan Kara
[RFC][PATCH] Journal superblock update should send a barrier
Hi, while reading through the checkpointing code I've realized that we actually have to send a barrier before each update of journal superblock after checkpointing. Attached patch does this. Just I'm not sure whether the performance cost won't be too big. In principle, we could make this more lightweight by using the fact that transaction commit also sends the barrier. So we could check before sending a barrier for transaction commit whether we are slowly running out of journal space and if ...
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Apr 22, 5:25 pm 2010
Steve Brown
Re: ext4 benchmark questions
The server is fully battery backed for up to 45 minutes. Also, LSI does provide tools to disable the cache when the BBU fails. Its one of the array config parameters. --
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Apr 23, 8:49 am 2010
Steve Brown
Re: ext4 benchmark questions
Thats good to know about the write barriers with WT cache. I'm still setting everything manually in /etc/fstab because, well... I don't always trust software. ;) The controller is an LSI 9280-8e (megaraid_sas kernel module). Drives are 1TB Seagate ES.2s, 16 of them in the chassis. Steve --
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Apr 23, 8:38 am 2010
Ric Wheeler
Re: ext4 benchmark questions
Barriers when working should never make things faster, at best, we should have parity. Also important to note that barriers should be disabled if you hardware RAID card exports itself as a "write through" cache, even if you enable barriers on the command line. What controller are you using and what kind of drives do you have in the back end? --
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Apr 23, 7:42 am 2010
Ric Wheeler
Re: ext4 benchmark questions
If you have the boot time log messages for the disks you use, you can see how the cache is advertised to the kernel. Also note that having battery backed RAID cards does not mean that your drive's write cache will survive a power outage. You need to use vendor specific tools usually to poke at the drives and make sure that the write cache on the S-ATA disks is properly disabled (unless the LSI firmware does something to manage the write cache on the drives). Thanks! Ric --
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Apr 23, 8:45 am 2010
Lukas Czerner
Re: [PATCH 2/2] Add batched discard support for ext4.
Well, it strongly depends on how is the file system fragmented. On the fresh file system (147G) the initial ioctl takes 2 seconds to finish (it may be worth to mention that on another SSD (111G) it takes 56s). I will try to get some numbers for the "usual" file system (not full, not I do not know much about how production system is being used, but I doubt this is that big issue. Sure the initial ioctl takes long to finish and there is a place for improvement, there was a proposal to do the ...
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Apr 23, 1:23 am 2010
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