Messages in this thread |  | | | Date | Mon, 30 Mar 2009 12:30:17 -0400 | | From | Mark Lord <> | | Subject | Re: Linux 2.6.29 |
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Linus Torvalds wrote: > > On Mon, 30 Mar 2009, Ric Wheeler wrote: >> A modern S-ATA drive has up to 32MB of write cache. If you lose power or >> suffer a sudden reboot (that can reset the bus at least), I am pretty sure >> that your above assumption is simply not true. > > At least traditionally, it's worth to note that 32MB of on-disk cache is > not the same as 32MB of kernel write cache. > > The drive caches tend to be more like track caches - you tend to have a > few large cache entries (segments), not something like a sector cache. And > I seriously doubt the disk will let you fill them up with writes: it > likely has things like the sector remapping tables in those caches too. ..
I spent an entire day recently, trying to see if I could significantly fill up the 32MB cache on a 750GB Hitach SATA drive here.
With deliberate/random write patterns, big and small, near and far, I could not fill the drive with anything approaching a full second of latent write-cache flush time.
Not even close. Which is a pity, because I really wanted to do some testing related to a deep write cache. But it just wouldn't happen.
I tried this again on a 16MB cache of a Seagate drive, no difference.
Bummer. :)
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