Booting into SSD ExpressCache possible?

potuz · Guru Joined: 30 Jan 2010 Posts: 378

I'm thinking on getting a laptop similar to this one here

http://wiki.gentoo.org/wiki/Samsung_Series_5_Ultra_530U3C-A02PT

which comes with a small SSD 24Gb which is used as a cache for windows booting (SanDisk ExtremeCache) but it's big enough to hold a gentoo installation. I've never had such a machine but since the kernel recognizes de SSD as a SATA device then I figured I can reformat it and install the kernel there. I don't have any use for windows, but I wander if I can wipe it out entirely and boot from that SSD or the BIOS won't allow to boot from that drive?

eccerr0r · Posted: Sat Jun 22, 2013 5:25 am Post subject:

I have one of those machines with the Intel Rapid Start Technology/Cache.

Yes this does show up as a regular disk, and well, though I have not really messed with it, I don't think it's bootable because of BIOS.
If your BIOS can change boot drives all the better...

I'm not even using that disk right now, it still has a hibernation partition on it (unused) and the rest of it is a ext3fs for me...

The machine behaves very unhappy under Linux when it suspend/resumes. I still have yet to figure out why...
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Intel Core i7 2700K/Radeon R7 250/24GB DDR3/256GB SSD
What am I supposed watching?

potuz · Guru Joined: 30 Jan 2010 Posts: 378

Thanks for the reply. I imagined that suspend/resume could be not nice with rapidstart. I've seen reports where people say it does work fine. I guess I'll have to wait and see. As for booting, I figured that in the worst case scenario I can have the bootloader in sda (the hard drive) and from there try to boot a kernel in sdb1 (the iSdd drive).

eccerr0r · Posted: Sat Jun 22, 2013 3:10 pm Post subject:

When I looked at this a while ago I didn't see any compatibility software for linux and windows to share the cache - that would have been the best solution. I couldn't even get that disk repartitioned for Windows when the cache was enabled.

I ended up disabling the cache and getting a SSD to replace the HDD...
_________________
Intel Core i7 2700K/Radeon R7 250/24GB DDR3/256GB SSD
What am I supposed watching?

potuz · Guru Joined: 30 Jan 2010 Posts: 378

salahx · Guru Joined: 12 Mar 2005 Posts: 530

I'm not sure if you can boot from it (probably not), while Linux doesn't support ExpressCache, the current Linux kernel (3.9) supports dm-cache, and the next version of Linux kernel will support bcache, both of which are similar in purpose (but are not compatible with) ExpressCache.

A word of warning, however: While with dm-cache you can take an existing an existing volume and add a cache, this is NOT the case with bcache - the origin and cache volumes must be formatted as bcache volume (obliterating any existing data).

eccerr0r · Posted: Fri Jun 28, 2013 7:42 pm Post subject:

That was sort of the nice thing with using the Intel "fake fake raid" system using BIOS (fake raid, as in BIOS RAID. Fake fake raid as in, cache raid using BIOS) - you can get boot sectors from the cache system. If you don't flush out the boot sectors cached on the ssd... and you'll get really fast boot times. If you never use a piece of software on the HDD? all of that will expire from the cache and your most frequently used stuff will be copied to it.

This is the hope, have Linux on the HDD, use it enough and it all gets cached off of the SSD and backed by the HDD. Stuff you don't use often, including Windows, will stay on the HDD only, but you can still access and use it like a normal disk. This theoretically is possible as SRT is supposedly LBA level caching. Now knowing how/where the tags are stored is a mystery... so no software support :( I suspect it'd be part of the dm-raid system someday if it is possible...
_________________
Intel Core i7 2700K/Radeon R7 250/24GB DDR3/256GB SSD
What am I supposed watching?

potuz · Guru Joined: 30 Jan 2010 Posts: 378

I finally got the machine here. No problems in installing and booting a kernel off the ssd. The setup was simply to have a small EFI partition and /home on the HD (along with portage tmp directory to protect the SSD) and let / and /boot be at the SSD. Grub2 on the EFI partition has no problem in booting the kernel in the SSD and it's working quite fast.