[SATLUG] fileserver SATA + RAID question
eli at then7.com
Sun Jul 17 16:54:34 CDT 2005
lvm is pretty cool, but not something i need.
when using expensive scsi 15,000RPM drives and expensive redundant scsi
raid controllers, upgrading the array quickly and cheaply is a problem. I
could see how LVM allows one to simply build a second array on the system
and add the space to the existing lvm volume.
with commodity hardware, i wouldn't bother with lvm. i just get on
newegg.com, order a few 400gb pata drives for $258 ea. shipped, build a
new replacement array, move the data over, and be done with it. rsync will
move the bulk of the data over while the primary system is still
running(at non peak hours). then pick a time to pull the system offline,
and rsync the last bit of data that has changed, swap the drives and your
total down time? 5 to 10 minutes.
so lvm isn't particularly interesting to me currently, but i think it's
neat and useful in other situations. raid5 software raid works great imo,
and with todays proccessors, cpu usage isn't a concern of mine. it's
flexible and does exactly what i want it to do. i've tested it robustness
by pulling drives, i've benchmarked it using up to 32 simultaneous
read/writes, i've done rebuilds on degraded arrays, and no problems.
i don't normally raid5 my /boot partition (the partition that holds the
kernel). i just mirror it (raid 1).
Everything else i raid 5.
Performance is more then acceptable, with the bottleneck being ide drives
(sata or pata). If I wanted more i/o, i'd go with inexpensive scsi
non-raid controllers, adaptec is fine among others, and use some 10k rpm
I've spent quite a bit of time using linux software raid, and recommend it
if you got the time and experience.
Going with hardware raid is always an alternative though, we've got the
3ware card running raid 5, and it's been flawless, has nice features, and
abstraction of the raid device is a very good thing. It's the way to go if
you got the spare bucks and not to much time learning linux software raid,
and or just want something easy that works good.
one thing i do avoid is cheap psuedo raid chipsets that come on mobos and
pci cards (the ones that do xor on the host cpu, not on the chipset
Much better to buy a true hardware raid card like the 3ware, or simply use
linux software raid on vanilla ide channels.
> On Sun, 17 Jul 2005 10:23:02 -0500, tweeks <tweeksjunk2 at theweeks.org>
>>Maybe I should do a talk at SATLUG/XCSSA on using software RAID w/LVM.
>>much easier than it sounds.
> Please do. The stacking of software RAID and software drive
> virtualization (LVM) on commodity drives makes me somewhat
> uncomfortable. Even if the performance is OK, I fear it turning into a
> write-only filesystem. How does one recover data when a critical LVM
> table or other single point of failure gets hosed? --Don
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