Ed> Hi, repeat of an older question I asked some months back. Looking Ed> to add BBU writeback "HBA" to run software raid over the top. So Ed> ideally I want either a raid controller which can pretend to be an Ed> HBA with 4 individual drives each with writeback cache (and a Ed> battery). Or at a pinch I would accept a controller which can Ed> offer 2 pairs of RAID-1 with writeback cache and I would run linux Ed> raid-0 (or XFS storage groups) over the top - caveat that I would Ed> very much desire that if the hardware controller fails I can pull Ed> the individual raid-1 drives out and access them from a vanilla Ed> motherboard controller? Once you use a HW Raid controller like this, you're not going to be able to just pull them out and use them with a vanilla controller. Well... maybe if you just expose them as JBODs, but then I doubt there will be any BBU of the devices, or caching, but that's very vendor specific. Why not just get a UPS for your server instead? And monitor the UPS and shutdown the server if there's a long (enough) outage to worry about? Ed> The goal is to be able to safely enable writeback caching on a 4 Ed> drive RAID10 (or XFS over raid-1), but if the controller should Ed> fail (or even just an urgent need to access the data from a second Ed> machine) then I can access the arrays from another machine which Ed> doesn't have such a controller. Operating system is a recent linux Ed> 3 kernel I think a UPS is a better bet. Ed> Can anyone comment on whether such a hardware card exists (seems Ed> it's hard to get writeback caching on drives *and* have those Ed> drives readable without the same controller present). Currently Ed> eyeing up the Areca 1882 8 port unit - thoughts? Instead of going down this route, just get a UPS and add more memory to the system you can cache more of the filesystem in memory. Then you can also have multiple controllers so as to spread the load out. The increase in performance by adding BBU isn't going to be all that much from my experience. If anything, adding more spindles will give you more performance. But you're not clear about your workload, whether it's large numbers of small files all over the place or fewer by larger files? Compile box? Compute node? Home directory server? John -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
