Messages in this thread | | | Date | Wed, 18 Apr 2007 13:39:47 -0400 | From | Jeff Garzik <> | Subject | Re: ZFS with Linux: An Open Plea |
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Lennart Sorensen wrote: > On Mon, Apr 16, 2007 at 10:18:45PM +0200, Tomasz K?oczko wrote: >> Of cources it can be true in most cases (probably for some more advanced >> RAID controlers). Few weeks ago I perform some basic test on Dell 2950 >> with 8x73GB SAS disk .. just as for kill time (waiting for access to some >> bigger box ;). This small iron box have inside RAID controller (Dell uses >> in this box LSI Logic SAS MegaRAID based ctrl). Anykind combinations on >> controler level RAID was slower than using this as plain JBOD with LVM or >> MD+LVM. Diffrence between HW and soft RAID was not so big (1-6% depending >> on configuration) but allways HW produces worser results (don't ask me >> why). Finaly I decide using this disk as four RAID1 luns only because >> under Linux I can't read each phisical disk SMART data and protecting this >> by RAID on controller level and collecting SNMP traps from DRAC card was >> kind of worakaround for this (in my case it will be better constanlty >> monitor disk healt and collesting some SMART data for observe trends on >> for example zabbix graphs for try predict some faults using triggers). On >> top of this was configured diffrent types of volumes on LVM level (some >> with stripping some without, some with bigger some with smaller chunk >> size). > > Does it matter that google's recent report on disk failures indicated > that SMART never predicted anything useful as far as they could tell? > Certainly none of my drive failures ever had SMART make any kind of > indication that anything was wrong. > > I think the main benefit of MD raid, is that it is portable, doesn't > lock you into a specific piece of hardware, and you can span multiple > controllers, and it is likely easier to have bugs in MD raid fixed that > in some raid controller's firmware if any were to be found. Performance > advantages are a bonus of course.
SMART largely depends on how you use it. Simply polling the current status will not give you all the benefits SMART provides. On the dedicated servers that I rent, running the extended test ('-t long') often finds problems before you start losing data, or deal with a drive death. Certainly not a huge sample size, but it backs up what I hear in the field. Running the SMART tests on a weekly basis seems most effective, though you'll want to stagger the tests if running in a RAID set.
Jeff
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