Re: SSDs in RAID and bio(4)
On Fri, Oct 18, 2013 at 09:04:55PM -0700, Chris Cappuccio wrote: Darren Spruell [phatbuck...@gmail.com] wrote: I don't have a great deal of experience with SSD disks but was spec'ing some systems to use them. We'd be doing RAID on the hosts and I'd prefer to have something supported by bio(4) for volume management. Do SSDs have any impact on ability to do this? Or can one use the same HW RAID controllers for volume management and bio(4) doesn't have to deal with any differences? Or do SSDs typically require special RAID controllers? Looking at Dell R420s and hoping the PERC controller + SSD combination will work under bio(4) (although knowing precisely the driver/controller would be necessary, I realize). SSDs mimic the same interface of any hard disk, bioctl doesn't treat them any differently than any other disk. Using them in RAID isn't typically the best idea, if you are worried about write failures bringing the disks to a halt. At least, some failure modes will affect all SSDs *at the same time* in a RAID configuration because the SSDs all receive a similar number of write requests and data. If the softraid develops TRIM support then you'll get better write performance (although if I'm reading right, some modern SSDs use tricks to minimize the need for TRIM?) Yes, the modern SSDs run periodic tasks to reduce the impact of the lack of TRIM support and to enhance the speed. I waited until, uhh, now just to use SSDs in server applications. And I'm still only counting on them lasting for 2 or 3 years -- Juan Francisco Cantero Hurtado http://juanfra.info
Re: SSDs in RAID and bio(4)
On 2013-10-19, Chris Cappuccio ch...@nmedia.net wrote: (although if I'm reading right, some modern SSDs use tricks to minimize the need for TRIM?) If they can do that, they'd have to understand the filesystem. Seems like a bit too much magic to have on the ssd controller..
Re: SSDs in RAID and bio(4)
Darren Spruell [phatbuck...@gmail.com] wrote: I don't have a great deal of experience with SSD disks but was spec'ing some systems to use them. We'd be doing RAID on the hosts and I'd prefer to have something supported by bio(4) for volume management. Do SSDs have any impact on ability to do this? Or can one use the same HW RAID controllers for volume management and bio(4) doesn't have to deal with any differences? Or do SSDs typically require special RAID controllers? Looking at Dell R420s and hoping the PERC controller + SSD combination will work under bio(4) (although knowing precisely the driver/controller would be necessary, I realize). SSDs mimic the same interface of any hard disk, bioctl doesn't treat them any differently than any other disk. Using them in RAID isn't typically the best idea, if you are worried about write failures bringing the disks to a halt. At least, some failure modes will affect all SSDs *at the same time* in a RAID configuration because the SSDs all receive a similar number of write requests and data. If the softraid develops TRIM support then you'll get better write performance (although if I'm reading right, some modern SSDs use tricks to minimize the need for TRIM?) I waited until, uhh, now just to use SSDs in server applications. And I'm still only counting on them lasting for 2 or 3 years
SSDs in RAID and bio(4)
I don't have a great deal of experience with SSD disks but was spec'ing some systems to use them. We'd be doing RAID on the hosts and I'd prefer to have something supported by bio(4) for volume management. Do SSDs have any impact on ability to do this? Or can one use the same HW RAID controllers for volume management and bio(4) doesn't have to deal with any differences? Or do SSDs typically require special RAID controllers? Looking at Dell R420s and hoping the PERC controller + SSD combination will work under bio(4) (although knowing precisely the driver/controller would be necessary, I realize). -- DS
