Richard Fish wrote: > On 3/2/06, Marton Gabor <[EMAIL PROTECTED]> wrote: >>let's say a ~100MB /boot in RAID1, 512MB swap not in RAID on every disk,
Actually, if you make 512MB "non-raid" swap on each disk with equal priority, its like having swap on raid0 (it will be stripped over swap-partitions on all disks). But disadvantage is, that if swap is used and some of your disks fails, your system probably crushes and will have to be restarted. If stability is your concern, you could maybe think about swap on raid1. In such a case you would survive disk failure even if swap had been already used (because it is be mirrored too). > You should also consider what kind of IO throughput you require from > this system. RAID5 will require an IO to every drive for each write > operation. Additionally, reads can only be satisfied by a single > drive. This means your write performance will max out at around > 33MB/s, and reads will max out at the speed of the disks (70MB/s > typical today) Frankly, I dont understand this. Why should the write speed be so degraded? If you have 4 disks in raid5, and you want to write 1.5 GB of data, you actually write 500MB on disk1, 500MB on disk2, 500MB on disk3 and 500MB on disk4 (1.5 GB data + 0.5 GB parity). And because they are sata-disks, they do not share i/o channel, as 2 pata-disks on one cable. In other words, write operations are parallel. There is of course some overhead caused by parity calculation and synchronisation, but with today's cpu it is not problem. I'm sure with 4 todays equal sata disks read/write speed of raid5-array would be much higher... > either RAID1 set, so you should easily be able to saturate the bus > bandwidth at 132MB/s. Nope. Today disks controllers are not attached to southbridge through pci, but rather through a few pci-express lines - 2, 4, or even more, depending on mobo configuration. For example nForce4 has 20 pci-express flexible lines, it means mobo-producers can use them as they want, but most cheap boards have 2pci-express lines assigned to sata disk controller). FYI, peak transfer rates: pci-express x1 = ~500MB/s unencoded data rate (1st gen. 250MB/s), 33MHz pci = 133 MB/s And moreover unlike pci, pci-express is bi-directional, at the same time data can be read/written... But the other (and rather sad) thing is pci-express and sata-II/NCQ support in linux... :-( Jarry -- gentoo-user@gentoo.org mailing list
