On Thursday 14 November 2024 17:00:07 GMT Dale wrote: > Michael wrote: > > On Wednesday 13 November 2024 23:10:10 GMT Dale wrote: > >> Howdy, > >> > >> One of my PVs is about 83% full. Time to add more space, soon anyway. > >> I try not to go past 90%. Anyway, I was looking at hard drives and > >> noticed something new. I think I saw one a while back but didn't look > >> into it at the time. I'm looking at 18TB drives, right now. Some new > >> Seagate drives have dual actuators. Basically, they have two sets of > >> heads. In theory, if circumstances are right, it could read data twice > >> as fast. Of course, most of the time that won't be the case but it can > >> happen often enough to make it get data a little faster. Even a 25% or > >> 30% increase gives Seagate something to brag about. Another sales tool. > >> > >> Some heavy data users wouldn't mind either. > >> > >> My question is this. Given they cost about $20 more, from what I've > >> found anyway, is it worth it? Is there a downside to this new set of > >> heads being added? I'm thinking a higher failure rate, more risk to > >> data or something like that. I think this is a fairly new thing, last > >> couple years or so maybe. We all know how some new things don't work > >> out. > >> > >> Just looking for thoughts and opinions, facts if someone has some. > >> Failure rate compared to single actuator drives if there is such data. > >> My searched didn't help me find anything useful. > >> > >> Thanks. > >> > >> Dale > >> > >> :-) :-) > > > > I don't know much about these drives beyond what the OEM claims. From > > what I read, I can surmise the following hypotheses: > > > > These drives draw more power from your PSU and although they are filled > > with helium to mitigate against higher power/heat, they will require > > better cooling at the margin than a conventional drive. > > > > Your system will use dev-libs/libaio to read the whole disk as a single > > SATA drive (a SAS port will read it as two separate LUNs). The first 50% > > of LBAs will be accessed by the first head and the last 50% by the other > > head. So far, so good. > > > > Theoretically, I suspect this creates a higher probability of failure. In > > the hypothetical scenario of a large sequential write where both heads > > are writing data of a single file, then both heads must succeed in their > > write operation. The cumulative probability of success of head A + head B > > is calculated as P(A⋂B). As an example, if say the probability of a > > successful write of each head is 80%, the cumulative probability of both > > heads succeeding is only 64%: > > > > 0.8 * 0.8 = 0.64 > > > > As long as I didn't make any glaring errors, this simplistic thought > > experiment assumes all else being equal with a conventional single head > > drive, but it never is. The reliability of a conventional non-helium > > filled drive may be lower to start with. Seagate claim their Exos 2 > > reliability is comparable to other enterprise-grade hard drives, but I > > don't have any real world experience to share here. I expect by the time > > enough reliability statistics are available, the OEMs would have moved on > > to different drive technologies. > > > > When considering buying this drive you could look at the market segment > > needs and use cases Seagate/WD could have tried to address by developing > > and marketing this technology. These drives are for cloud storage > > implementations, where higher IOPS, data density and speed of read/write > > is > > desired, while everything is RAID'ed and backed up. The trade off is > > power > > usage and heat. > > > > Personally, I tend to buy n-1 versions of storage solutions, for the > > following reasons: > > > > 1. Price per GB is cheaper. > > 2. Any bad news and rumours about novel failing technologies or unsuitable > > implementations (e.g. unmarked SMRs being used in NAS) tend to spread far > > and wide over time. > > 3. High volume sellers start offering discounts for older models. > > > > However, I don't have a need to store the amount of data you do. Most of > > my drives stay empty. Here's a 4TB spinning disk with 3 OS and 9 > > partitions: > > > > ~ # gdisk -l /dev/sda | grep TiB > > Disk /dev/sda: 7814037168 sectors, 3.6 TiB > > Total free space is 6986885052 sectors (3.3 TiB) > > > > HTH > > Sounds like my system may not can even handle one of these. I'm not > sure my SATA ports support that stuff.
I think your PC would handle these fine. > It sounds like this is not something I really need anyway. Well, this is more to the point. ;-) > After all, I'm already spanning my data > over three drives. I'm sure some data is coming from each drive. No > way to really know for sure but makes sense. > > Do you have a link or something to a place that explains what parts of > the Seagate model number means? I know ST is for Seagate. The size is > next. After that, everything I find is old and outdated. I looked on > the Seagate website to but had no luck. I figure someone made one, > somewhere. A link would be fine. This document is from 2011, I don't know if they changed their nomenclature since then. https://www.seagate.com/files/staticfiles/docs/pdf/marketing/st-model-number-cheat-sheet-sc504-1-1102us.pdf > Thanks. > > Dale > > :-) :-) The only Seagate 7200RPM disk I have started playing up a month ago. I now have to replace it. :-(
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