support for physical ramdisk
I stumbled upon bcache today and was wondering, how would this work with a physical ramdisk instead of a SSD? --
To unsubscribe from this list: send the line "unsubscribe linux-bcache" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
A message that is not in the archive (sent off-list or not yet received): [email protected]
It'd function, but performance would be worse than just using the pagecache, bcache does a whole lot of extra work to get around the limitations of SSDs and the pagecache is blazing fast. Why would you want to do that?
Quoted 7 lines · Cory Coager
I stumbled upon bcache today and was wondering, how would this work with a physical ramdisk instead of a SSD?
--
To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
A message that is not in the archive (sent off-list or not yet received): AANLkTik30_V_bWGsvoUQw-5-W7URK1tSTDSfcTa8LayX-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org
I was hoping to enable write back with the use of a battery backed ramdisk. I'm simply substituting the SSD for a physical ramdisk. The ramdisk would outperform the SSD and would probably be safer during power loss than a SSD (assuming the battery is in good condition).
Quoted 4 lines · Kent Overstreet
It'd function, but performance would be worse than just using the pagecache, bcache does a whole lot of extra work to get around the limitations of SSDs and the pagecache is blazing fast. Why would you want to do that?
--
To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
A message that is not in the archive (sent off-list or not yet received): [email protected]
A message that is not in the archive (sent off-list or not yet received): AANLkTinUD1_z3iZ3VgJFh=JkF+6EWDq62==Z9EhBpwBP-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org
I would think even a low end DDR2 module would saturate the SATA interface bandwidth.
How would external journal to bcache help?
Quoted 6 lines · Kent Overstreet
Ahh, that makes sense. I'd be curious what performance you get - it certainly wasn't designed with ram in mind. You'll want to play around with the bucket size and see what works best, too.
Also, in the future I'm going to add support for an external journal to bcache - that could be the best of both worlds, for you.
--
To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
A message that is not in the archive (sent off-list or not yet received): [email protected]
Quoted 4 lines · Cory Coager
I would think even a low end DDR2 module would saturate the SATA interface bandwidth.
How would external journal to bcache help?
Well, ram is more expensive per gigabyte than SSDs, particularly if you've got something with a battery attached - the idea would be to use your SSD for buffering 80 gb or so of writes, but then buffer all of bcache's metadata writes in battery backed-up ram, significantly decreasing the number of write IOPS to the SSD, and making it so pretty much all the writes to the SSD are big contiguous writes.
Quoted 10 lines · Kent Overstreet
Quoted 7 lines
Ahh, that makes sense. I'd be curious what performance you get - it certainly wasn't designed with ram in mind. You'll want to play around with the bucket size and see what works best, too.
Also, in the future I'm going to add support for an external journal to bcache - that could be the best of both worlds, for you.
--
To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
A message that is not in the archive (sent off-list or not yet received): AANLkTin+xKeYbxSU6u=h8bfujSpm3fxqurC0nR4+89wX-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org
Sounds great, when will it be ready? ;-)
Quoted 6 lines · Kent Overstreet
Well, ram is more expensive per gigabyte than SSDs, particularly if you've got something with a battery attached - the idea would be to use your SSD for buffering 80 gb or so of writes, but then buffer all of bcache's metadata writes in battery backed-up ram, significantly decreasing the number of write IOPS to the SSD, and making it so pretty much all the writes to the SSD are big contiguous writes.
--
To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
A message that is not in the archive (sent off-list or not yet received): [email protected]
Quoted 1 line · Cory Coager
Sounds great, when will it be ready? ;-)
Well, good question. I've been short funding and thus time for bcache lately; not sure what's happening there just yet.
And there's a bunch of things on my todo list; my main priority has been the code for a bcache specific block device and superblock for the backing device. After that is multiple cache devices, volume management and tiered storage, but there's no set order those and journalling/external journal support need to be done in.
Quoted 8 lines · Kent Overstreet
Quoted 6 lines
Well, ram is more expensive per gigabyte than SSDs, particularly if you've got something with a battery attached - the idea would be to use your SSD for buffering 80 gb or so of writes, but then buffer all of bcache's metadata writes in battery backed-up ram, significantly decreasing the number of write IOPS to the SSD, and making it so pretty much all the writes to the SSD are big contiguous writes.
--
To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html