Am Tue, 16 May 2017 14:21:20 +0200 schrieb Tomasz Torcz <to...@pipebreaker.pl>:
> On Tue, May 16, 2017 at 03:58:41AM +0200, Kai Krakow wrote: > > Am Mon, 15 May 2017 22:05:05 +0200 > > schrieb Tomasz Torcz <to...@pipebreaker.pl>: > > > [...] > > > > > > Let me add my 2 cents. bcache-writearound does not cache writes > > > on SSD, so there are less writes overall to flash. It is said > > > to prolong the life of the flash drive. > > > I've recently switched from bcache-writeback to > > > bcache-writearound, because my SSD caching drive is at the edge > > > of it's lifetime. I'm using bcache in following configuration: > > > http://enotty.pipebreaker.pl/dżogstaff/2016.05.25-opcja2.svg My > > > SSD is Samsung SSD 850 EVO 120GB, which I bought exactly 2 years > > > ago. > > > > > > Now, according to > > > http://www.samsung.com/semiconductor/minisite/ssd/product/consumer/850evo.html > > > 120GB and 250GB warranty only covers 75 TBW (terabytes written). > > > > According to your chart, all your data is written twice to bcache. > > It may have been better to buy two drives, one per mirror. I don't > > think that SSD firmwares do deduplication - so data is really > > written twice. > > I'm aware of that, but 50 GB (I've got 100GB caching partition) > is still plenty to cache my ~, some media files, two small VMs. > On the other hand I don't want to overspend. This is just a home > server. > Nb. I'm still waiting for btrfs native SSD caching, which was > planned for 3.6 kernel 5 years ago :) > ( > https://oss.oracle.com/~mason/presentation/btrfs-jls-12/btrfs.html#/planned-3.6 > ) > > > > > > > > My > > > drive has # smartctl -a /dev/sda | grep LBA 241 > > > Total_LBAs_Written 0x0032 099 099 000 Old_age > > > Always - 136025596053 > > > > Doesn't say this "99%" remaining? The threshold is far from being > > reached... > > > > I'm curious, what is Wear_Leveling_Count reporting? > > ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE > UPDATED WHEN_FAILED RAW_VALUE 9 Power_On_Hours 0x0032 > 096 096 000 Old_age Always - 18227 12 > Power_Cycle_Count 0x0032 099 099 000 Old_age > Always - 29 177 Wear_Leveling_Count 0x0013 001 > 001 000 Pre-fail Always - 4916 > > Is this 001 mean 1%? If so, SMART contradicts datasheets. And I > don't think I shoud see read errors for 1% wear. It more means 1% left, that is 99% wear... Most of these are counters from 100 down to zero, with THRESH being the threshold point below or at which it is considered failed or failing. Only a few values work the other way around (like temperature). Be careful with interpreting raw values: they may be very manufacturer specific and not normalized. According to Total_LBAs_Written, the manufacturer thinks the drive could still take 100x more (only 1% used). But your wear level is almost 100% (value = 001). I think that value isn't really designed around the flash cell lifetime, but intermediate components like caches. So you need to read most values "backwards": It's not a used counter, but a "what's left" counter. What does it tell you about reserved blocks usage? Note that it's sort of double negation here: value 100 used means 100% unused or 0% used... ;-) Or just insert a "minus" in front of those values and think of them counting up to zero. So on a time axis it's at -100% of the total lifetime scale and 0 is the fail point (or whatever "thresh" says). -- Regards, Kai Replies to list-only preferred. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
